Microwave gel heat pad...

[Simpo Two]

I damaged my left thumb last year and the physio recommended a 'wheatibag' twice a day to apply heat. It helps but is cumbersome and gradually loses efficiacy as it dries out. The heating is uneven too, so there are parts too hot and parts not hot enough..

Is there a microwave gel pad but in tube form so I can just stick my thumb in it? Thanks!