If the glasses or goggles don't leak, they're going to fog up, so it's a Catch 22. I don't see how anybody rides in a rain that amounts to anything...the rain drops sting when hitting your face!
There's really no place to store a 3/4 or a Flip/Full face helmet other than in a King TP. If you don't have a TP, I suppose a large rack bag would be another choice.
Just wear the FF helmet (I'd get a Flip Face like the Nolan N-104, Shoei Neotec, or Schuberth C3...Or a Shark Evo III) and store the Tupperware Bowl until you get where you're going.
I personally find a 1/2 Helmet to be MUCH more uncomfortable than wearing a Flip Face. Sun Burn, Wind Burn, and just the hot wind hitting my face at 80mph is not comfortable for me...not to mention when it's cold outside. The full coverage just has more positives than negatives for me.
The unique thing about the Shark Evo III is that it's the only flip face helmet that I know of that converts into a true 3/4 helmet when desired. It makes it kind of nice at times, like riding in heavy, slow moving traffic. The downside to the Shark is that it's bit heavier due to the mechanism. Everything is a trade off to some extent...