Lots of options don't really coexist with fast route-planning I'm afraid. Basically cycle.travel pretty much pre-calculates all the best routes (which takes a couple of days each time), and the reason it's so fast is because it can call on those pre-calculations. For each extra option I'd have to pre-calculate another dataset, and rent a new server to store them on. I've got two options so far (normal and paved-only) and might add a third to prefer gravel/off-road, but after that it gets expensive!
But - what you can do is open up the elevation display as you drag the route around. It updates live as you drag, so you can see how your changes are affecting the profile. Once you get the hang of it you can work out flat or hilly routes that way fairly easily.