Theres a Torchwood/SPN/DrWho(10th)-Crossoverfic out there with Dean and Cas making out at one point. Its from before the fifth SPN-Season I think. It isnt as awesome as your stuff but when I originally found it, I liked it. In the end there are some weaknesses but maybe you can find a bit inspiration there. So here's the first of eleven parts: http://ravengrimm.livejournal.com/3866.html