Very likely there are more than two ways, I understand how the one(s) you suggest is/are the right one(s) and any other one not proposed by you is wrong, by definition.
Only as an example, likely the solution you provided here (making use of VLANs) could be adapted as well:
http://forum.mikrotik.com/t/mikrotik-as-secondary-router-one-lan-port-bridged-to-wan/176360/1
Standard or non-standard matters little, whatever works, if it works, it works, and - specifically - I don’t think that the traffic between the PC and a printer needs to be optimized for efficiency, speed or bandwidth.
We don’t know if adding a route/accessing the ISP router is possible, and I have no idea if what works on “normal” ether would work on the real setup because of the wireless link.
But - for the sake of the reasoning - if it would be necessary to create a second bridge on the Mikrotik (even if it is “wrong”, it has no hardware offload, etc., etc.) I wouldn’t see it as a problem.
I see much more as possible issues (it depends on the printer and its drivers) if there are a sh*tload of strange protocols going on the network link, some network printers (and their drivers) are often too smart for their own good.