Hi Adam,
I am afraid your suggested brute force approach would be the standard way.
You could replace it by using a custom function module to go through all relevant infotypes in the last column of T77PR.
In any case: waych out for performance. Huge object lists in structural authorisations kill performance.So, either try to keep the lists reasonably short (not taking all object types, but only those really required for each role) or check out the authorisation BAdIs. I assume you should find a method there to avoid the exercise all together and achieve better performance at the same time. But I haven't used it for exactly that context yet, so can"t guarantee you'll be lucke with the BAdIs.
best wishes
Sven