You could always screw on the wall 16 or 32 inch board strip that would be screwed into studs. That way you don't have to compromise on the horizontal bike positioning. But if you have light bike, then you might even place the hanger in between the studs but you should use those butterfly wall hanger gizmos you can get in any hardware store. Those 'open' behind the drywall and have quite large surface pressure distribution on the back of the drywall.
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If you make your own home made hangers like in the post I linked to, you could even cut a horizontal slot into the drywall, say 2x2" and insert a piece of wood behind the drywall through this slot and attach the hanger to it. Most skilled hobbyists would know how to go about this. The plywood hanger would be made large enough to hide the hole and the screws holding the backplate in place.
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Just had an alternative idea for those worried about the forces on the crank. You could make that wood strip that the bike wheels rest on an L shaped bracket (to make sure wheels can't easily slip off it) and use a bungee cord around the top tube of the bike frame to hold it in the desired angle from the wall (or a strap of wood hinged on the wall that you lift and hook on the bike frame top tube) . However this wouldn't work that well for the upper bike since you might not be able to reach that high to secure the cord or some other mechanism (that is, unless you are an ingenious kind
).