You could use the event from the canal mod, the suez one that gives money over a couple of years ->
It's not an easy job, and it would mean you get a pop-up every month, but it's doable. I'll try to make it myself, to see if it works
Edit : Finally worked it out, but i got some good news and bad news.
The event fires every month, on every country and it reduces the CON of all pops by 1. These are the good news =)
Now, the bad ones. The event sometimes fires twice a month, and i can't figure out why (my modding skills ~ 0, at least with this game). The date at which it fires is random, you could get on the 1st or the 31th :-? Also, it's pretty annonying to have an event every month firing in your face with just an option.
I don't know if it's possible to make it invisible to player, maybe a more experienced modder can help

Also, new events would need to be created, i put the pandemic one at random =)