Don't do it! As small as the differences are, they are great in terms of machine tolerances. One of my friends had a portable Brother that had bobbins that were so close but not quite the same as my friends more expensive set up. Her life got much better once shes threw out all her bobbins and bought new ones. Marking the portable ones with a big black Sharpie X over them and leaving the set-up machine ones plain. I don't remember exactly but I think the wrong ones were the same diameter but just a shade taller/shorter than the others. Both bobbins fit in both machines and both caused problems!
The long arm set-up I used to use also used Type M bobbins. We found we couldn't wind a decent bobbin to save our lives and switched to prewound and vastly improved our stitch quality and happiness level. I think part of that was using a lighter weight bobbin thread than top thread, but a badly wound bobbin causes its own set of problems.
I've heard stories too though about machines that were too particular to use prewounds and the owners could only wind their bobbins on their own machines. I'd much prefer to buy prewounds, and I'm usually too cheap to do things like that. My current machine has an embroidery module but a proprietary bobbin, I know if I ever got an embroidery machine one of the features I would specifically want is a standard bobbin where I could get prewounds.