You could also use injectable b12, but to be honest not sure how much this will help. I remember Tokkyo stuff was thick and it turned out that it wasn't micronized very well, would still clog the pin. Not sure about supra?
Micronized refers the the thickness of the winstrol powder itself. If the suspension is thick because there is too much powder watering it down will help. If its because the powder is too thick it won't help you at all.
Do not use B12. I asked this question awhile back and found there is a limit to how much injectable B12 one can use without negative health effects. I don't remember exactly what they were but the person replying was quite knowledgeable on the subject and stated them exactly. Do a search if you can, maybe you'll find it.
Like others have stated sterile water is your best bet.