AaronOfBarbaria
Adventurer
Why not just implement a process by which the player rolls the d20 for the target's saving throw and announces to the DM what the highest save-bonus that is affected is?Your character wants to do something? You should be responsible for its full execution.
I.e. a characters casts thunderwave against an orc, rolls 2d8 +1d20 scoring 11 damage and a save roll of 4, then looking at their spell save DC of 13 to see that it would take a +9 save modifier for the orc to pass the save and says "I hit a +8 constitution save, 11 thunder damage, or half if I missed."