I train on rollers most of the time, some sessions spend half the time riding no handed whilst chatting on zwift, browsing online etc. I’ve also been known to do stupid dances on them 
I always advise that the bit where you’re nearly riding no handed, or indeed riding one handed is a lot sketchier than the actual riding no handed bit, so get past that bit ASAP and lean back into the no handed position. If it goes wrong I can generally unclip and get a foot down, although a couple of times the bike has got away and slid onto it’s side in the process. Don’t have anything sharp around and don’t be afraid to fall off and you’ll learn a lot quicker than being tense and worried 
My general advice is ‘kick it like you mean it!’ - meaning start with a powerful pedal stroke to get up to speed. Another thing that might help is riding slowly on the way to stopping, will get you used to riding slowly while you’re getting going. I sometimes ride rest intervals at around 30 cadence and it feels similar to starting the whole time…