Antiochus V said:Another alternative is to role-play slightly and use existing game mechanics.
-Arguably the qualities of an elite division are high experience and good equipment and access to support.
Experience comes from fighting. Thus a unit that has fought many battles might be renamed to a 'guards' division (I believe the soviets did this). To reflect its new status it can be given priority for upgrades, and could have some sort of brigade added to make it more potent.
Modification wise very little is required with this approach for a human player. An 'elite brigade' might be a way of adding the 'difference', and would be not be especially intrusive. However it is not possible to then add normal brigades.
The problem with adding elite units is that the designation of SS did not always imply quality, there were top quality SS and regular units, but there were also poor quality units of both.
What Antiochus V said - the best way is to role-play a bit. Create division, name it Waffen SS, upgrade it in the first row, before other units (to represent superior equipment), use it in important battles, so it can earn experience faster, reinforce it with top priority, give it the best brigades. And, basically, you'll achieve your goal.
In case of Soviets, it's a bit different. "Guards" were not created from the scratch. This name was given to battle-hardened divisions, which distinguished themselves more than others. So if you have a division that fought especially well or achieved something great, rename it "Guards" and then give it priority over the rest in upgrading, reinforcing ect.