I'd have to look at the code but you could probably force a dice roll and also force it hidden regardless of campaign settings so the players only see the shadow of the dice roll but it's not actually used. Doing that you wouldn't need to care what the dice roll showed (since you use the manual input value) but they'd think you did roll instead of input a roll.
Insanely busy right now so I can't poke at it but I'm pretty sure something like that is possible.