The problem with Createx is that the 'Reducer' besides being a thinner is also the catalyst that helps the paint dry faster and improve the finish. It might be difficult to find an alternative. Looks like you might need a heat gun as well.
I was scratching around and found these links. I hope these help Eviltoy...
http://www.stripersonline.com/surftalk/showthread.php?t=704899
http://www.airbrush.com/forums/tm.aspx?m=413108
http://www.kustomkulturelounge.com/forum/archive/index.php/t-2423.html
http://www.craigcentral.com/models/thinning.asp
http://www.airbrush.com/forums/tm.aspx?m=53715