I'm 5' 10" and often find myself feeling too far forward on the bike when riding the twisties in a more spirited fashion.
Same as that.
I read a post from someone, somewhere, who had a gel or foam insert fitted in the standard seat and had got the upholsterer to add a small 'wedge' in the front of the seat to avoid this slipping forward.
I've so far only made a half hearted attempt to get something like this done - I mailed three companies whose websites say they can do whatever you want to your seat - so far one has replied they they don't have gel inserts but if I can provide it they can fit it & the other 2 haven't bothered to reply.

I'll make another attempt soon & will let you know if I get something sorted