I recently found an adjustable Waterbottle Cage that will adjust to the size of your spray paint can.
Topeak Modula Ex Cage (Plastic Model) (see image below)
Topeak Modula Cage (Aluminum Model)
These are inexpensive ($6-$10) and work great on your measurement bike for holding a variety of sizes of bottles/cans. However, these do not open very wide so are best for sizes smaller than or equal to a regular waterbottle.
I purchased my from REI.com but just search the internet for the best prices.
