Take a toe strap (or similar) and it can be used to tie a wheel up to the hook. I managed to get a mountain bike with 3.0 knobblies onto a GWR train recently.
However, I refuse to bodge a way of hanging up a bike on a hook that someone has been paid good money to design and hasn't thought to investigate the variables it might have to cope with. Not even a little bit. I'd rather huff and puff to innocent train managers about it.
They'll be long with four spaces.
Most wheels (unless you're running box rims with tops 25mm tyres) can't hang in the hooks because there isn't enough space. Great designsss.
GWR staff can be some of the most arsey about it. I'd plan for splitting for the trains personally...
Edit: Wish so much I was coming... :(