To capture stereo I would like to attach a spare Sony ECM-MS2 I have to my JVC HM150. But the Sony is 24mm in diamater and the cylindrical clamp mount on the JVC is more suited for 19-21mm.

What options do I have or what would you guys recommend?

Attach some extender to the screw and use the original clamp mount?
Get something like the Rode SM5?

The OEM mount is probably not worth the trouble and cost of modifying. I would recommend the 'Rycote InVision Video - Shoe Foot 42901' which also isolates the mic from handling and camera/lens motor vibrations.
I'm sure you're aware a camera mounted mic is not good for picking up dialog, no matter what mount.. or mic.

Thanks Rick, I'll look into that one.

Yeah I know camaremounts are not optimum for dialog. I will use the Sony for location/ambient sound.
For other situations I use an AT3031 / AT835b on a rycote pistol grip.