Theme control for subsites

Just wondering if there is any way to control which themes each new site owner has access to. Basically, I'm trying to set up an automated blog/website service for local self-employed traders where each trade has a selection of custom themes.

For example, if a carpenter signs up he/she will have access to 5 themes perfect for a carpenter. If a dog walker signs up, they will have access to 5 themes for dog walkers etc etc.

Just wondering if this is possible at all.