Seen it mentioned in a few threads, just wanted to share this fix.
When unable to raise the bar, just brace to control the descent, as you would with negative dips or pull-ups. lower it not against your chest, but aim for belt/bellybutton. No need for a roll anymore, just sit up and voila!
or if you dont have a spotter just use dumbbells like a normal person...OR just ask someone whos taking a rest for a quick spot, but this will involve talking to someone IRL so yea just stick with DBs