Yes, but usually when there's a will there's a way.
Approach #1
One of the interesting things I noticed when testing the new declare_war event command is that it seems to bypass some of the normal DOW stuff so it's entirely possible (likely actually) that forcing a DOW via this command in an event would remove the need to have a claim. So I *think* that in fact the only one who can't easily get involved in that war right now would be a human player (because I excluded human player to avoid the possibility of spamming him with demands that are really geared towards the AI). I can easily rectify this (would take me less than 30 minutes to adjust).
Approach #2
At present the declare_war command doesn't accept a country tag as an argument, but I would guess that it would be a relatively trivial thing for Johan to add to the valid arguments in the code (if necesary, and as long as he didn't have to add error checking to it as well). If I'm correct, that would mean that I could script an event that checks if a specific tag owns Roma and then trigger the war via a string of events (a little like the ones I'm using for the crusades right now). Not very elegant, requires specific knowledge of who it need to check for, and requires one event per tag, but it could be done...
Approach #3
Another approach is to manufacture claims...easy for adjacent rulers but not so easy for anyone else. Fortunately I think that it might already be possible since I *think* that when Johan set up the argument for the declare_war effect he set it up as a valid [target character]. If that's the case (I would have to test it) then a character event could have the following:
Since in this instance whoever owns Roma would be the current target owner, it should be trivial to create an event that will spawn claims against whoever holds it. If that isn't the case, it would be a matter ten minutes or less for Johan to tie it into the valid character target file.
Approach #4
Except that I am rather smitten with the idea that if Byz takes Roma (certainly on the historic Patriarchs' wish lists
) they should get to keep it and recreate the Patriarchy of Roma. The Pope can relocate elsewhere (there are already events scripted and in place to handle that) and the game can continue on as normal.
Those are the ideas that come to mind immediately. There are probably a few other methods to achieve it too...

Approach #1
One of the interesting things I noticed when testing the new declare_war event command is that it seems to bypass some of the normal DOW stuff so it's entirely possible (likely actually) that forcing a DOW via this command in an event would remove the need to have a claim. So I *think* that in fact the only one who can't easily get involved in that war right now would be a human player (because I excluded human player to avoid the possibility of spamming him with demands that are really geared towards the AI). I can easily rectify this (would take me less than 30 minutes to adjust).
Approach #2
At present the declare_war command doesn't accept a country tag as an argument, but I would guess that it would be a relatively trivial thing for Johan to add to the valid arguments in the code (if necesary, and as long as he didn't have to add error checking to it as well). If I'm correct, that would mean that I could script an event that checks if a specific tag owns Roma and then trigger the war via a string of events (a little like the ones I'm using for the crusades right now). Not very elegant, requires specific knowledge of who it need to check for, and requires one event per tag, but it could be done...
Approach #3
Another approach is to manufacture claims...easy for adjacent rulers but not so easy for anyone else. Fortunately I think that it might already be possible since I *think* that when Johan set up the argument for the declare_war effect he set it up as a valid [target character]. If that's the case (I would have to test it) then a character event could have the following:
Code:
effect = { type = add_title_claim which = crusade_target_owner }
Approach #4
Except that I am rather smitten with the idea that if Byz takes Roma (certainly on the historic Patriarchs' wish lists
Those are the ideas that come to mind immediately. There are probably a few other methods to achieve it too...