Is there any way to let caster cast Stilled spells while prone/grappled like in PnP?

Now I'm guessing if Kaedrin knew a way how to and thought it was a good idea he'd have done it years ago, but I do wonder if it's possible.

I know this is a very old post, but the idea caught my attention...
I think it would be possible. You'd need a spell hook that checked for any effects on the character that would cause a prone condition. If they have any of those effects and have Still Spell, remove the effect. Go ahead and trigger the cast, and then re-apply the prone effect after they finish.
The problem with it would be duration of the re-applied effect. I'd have to give some thought on how to track the remaining duration so that I'd know how long to set the new effect for.