I'm also not entirely sure what the exact behaviour you want is, but assuming its that you want bar.meth1(42) to be equivalent to foo.meth1 being a classmethod of bar (with "self" being the class), then you can acheive this with:
meth1 = convert_to_classmethod(foo.meth1)
The problem with classmethod(foo.meth1) is that foo.meth1 has already been converted to a method, with a special meaning for the first parameter. You need to undo this and look at the underlying function object, reinterpreting what "self" means.
I'd also caution that this is a pretty odd thing to do, and thus liable to cause confusion to anyone reading your code. You are probably better off thinking through a different solution to your problem.