The trem bar is a great way to get quite wide and dramatic vibrato when doing a bend but of course you can do it without the bar - look at Yngwie - he does really wide vibrato when doing bends - sometimes up to a tone +- from the target but with precision oscillation between the two that makes it effective.
Like everything, you have got to start slow.
First do your bend up to the target pitch. Make sure it is at the correct pitch. Use your ears. There are few things worse than out of pitch bends.
I normally overbend first, then release to just below target and up/down again when I do vibrato on bends. What this means is, from the target pitch, increase your push a bit more so the pitch goes higher, then release so it comes in under and do this as many times as you like. It's easier than this sounds, but you have to start SLOW.