All things need to be done with caution, moderation and common sense. I would not heat up a full can. Nor would I put it close to an ignition source while heating. But when the can is perhaps half full (or less) I've put the in the sun and have also put them into a pan of hot water. On one can I saw this printed: "Danger - extremely flammable, contents under pressure, do not expose to temperatures exceeding 122 degrees." This raises an interesting advisory though - - that a person should probably not leave a spray paint can in a car in sun in the summer.
But you are probably right, there is some danger to heating the can and the danger increases as the can is more full. So, others should not try this.