Enter MobiMouse...
After poking around all afternoon on AppWorld, I finally managed to find something that does exactly what I want.
Its not free, but it allows me to control the mouse and so on on the laptop with a minimum of fuss - not the simplest of installs, with clients for both the phone and the pc, then a small bit of config to the pc's bluetooth setup, and then you're away!
Hope someone else finds this useful.