Network resources for non-domain PCs

I have a fair few users (mostly management) who primarily work for a different company within the same parent company who insist on using their existing company laptops when here. 

They have local accounts and want to access some domain resources - mostly CIFS shares. 

How do others in the same situation manage this?

It's becoming tiresome to map network drives for people, especially when infrastructure changes (as it just has to DFS based shares now).

I thought about perhaps a public share with various batch files to automatically mount drives for certain people, but that seems inefficient and perhaps exposes publically who has access to what. 

I should probably add that there is very little inclination to create domain trusts.

Thoughts?