On BHC you get a cast to help with momentum- FHC has no cast, so you need to get momentum elsewhere.
Typically one would do this by elevating their body, so, instead of the hips resting on the bar, it's their thighs resting on the bar. This way, when you fall forward there will be more weight on the front half of the bar causing you to fall/spin faster. The closer towards then knee caps you place the bar, the faster you'll spin - but it also gets tougher to wrap the bar, so you have to find a balance that works for you.
Then, you pike to wrap your hips around the bar once you've fallen long enough to generate some spin and voila.
here's a random example I found on youtube - you can see how the first thing she does it raise past her hips.
