Character on a Bicycle how together?

Then if you want one Skeleton and one Skinned mesh, combining the skeletal meshes might be your best option!

Just note that both objects will always be in the scene together regardless whether they are needed or not.

You can also come up with with custom animations where you 0 out the scale of your bike/character rig (based on your need).

Anything else is going to require a lot of manual setup to get around this issue.