[JeffMarmalade]

Yes absolutely. I'd suggest creating a "Shared services" stack, and put a MySQL service in that rack. Give it a static port (eg 3306).

Then create a second stack with Nginx or Apache (or both), and your choice of PHPs, as many as you need. All the sites will have access to MySQL from the first stack, on the port you configured (eg 3306).

Alternatively, do the "shared services" stack then add one stack per project. Just depends how you like to organise it.