We're making great progress on the rules for international FT though. Conor's involved in sorting out the international FT rules now, so he can't say there's no rules in FT anymore
The solution we've come up with for FT ( WFTF ) is that bean bags can only be used for the freestyle (sitting) position. For kneelers you can you nothing or you can use a kneeling roll (either your own, which must comply with the specified dimensions of a kneeling roll, or the roll provided on each kneeling lane).
It's very difficult (damn near impossible) to cheat when you're using a kneeling roll.
To the original OP, If you're shooting the NEFTA Winter League, you may have noticed that for every Winter League event this season, I've been using a kneeling roll on the kneelers.
The BFTA Rules are being changed this year to allow the use of a kneeling roll too (it's optional for BFTA events).
I think that's the answer to the kneeling problem - follow the lead of the WFTF and disallow the bean bag.
It also makes marshalling the kneeling lanes a doddle too. If the shooter is using a roll, there's no way you can sit on a turned foot, laces up/ laces down - doesn't matter because there's no advantage either way, and with a roll you can't gain any lateral support like you would do with a bag.
My kneeling roll weighs in at just 83g, I clip it to my bag and don't even notice I'm carrying it round with me.
I've also only missed one kneeling shot all season, and that was the 45 yarder high on the bank at Keighley and I think I missed for wind rather than stability.