The heatsink I attached for testing was a bit cumbersome, and was supported by the leads of the TO-220 transistor package and a bit of Blu-Tak.

To make things a little more sturdy I made a bracket from 3 mm thick aluminium angle.  This will attach to the PCB mounting holes using M2.5 screws.  On the back of the bracket I will attach three small heatsinks to increase the mass and surface area.  On the front the transistor will be attached with a standard isolating kit.  The fan will be attached with screws through the vanes of the small heatsinks.  I drew a sketch on some scrap paper then I decided to make a nice drawing with QCad.