I'm not a plumber either...but know bits/pieces. In some locales, a drain can be up to 6 feet from the vent...so if you had shower with in 6 feet of the vented lav, it works for the shower too. In fact I did this in my last house and it works fine.
BUT you would want to ask specifics like that of you local code officials...
when it comes to breakfast, the chicken is dedicated, the pig is committed.