Fortune/luck rolls in PbP
A question for the hive mind!
Are there any tips on how to handle "luck / fortune" roll mechanics, in games where a player can influence the outcome of a die, but must declare doing so before the die is rolled.
Such as where a player can have their PC do things like:
roll a d20, and then choose whether the attack uses the attacker’s roll or yours
replace any attack roll, saving throw, or ability check made by you or another creature
Because waiting for the player to say they will use or not use this cannot work (slows the game down way too much).
I have some ideas of how to adapt this:
for example letting the player use their power after the roll is made (which is a big boost since they know what the outcome of the roll is before switching it) but subjecting this to Fate: having a 50/50 chance that it works (to balance the added power).
My question is: has this been discussed somewhere? Are there PnB rules that work for this?