D2t is very thick, IMO. I have thinned it before (denatured alcohol, I think) and it worked fine. I would suggest a search for that. But yes, you can sometimes have an impact on the action from the additional weight of the clear. I've used Enviro-tech before (which is referred to as e-tex on this site quite a bit) and prefer it, primarily because it is thinner. However, E-tex takes several hours to cure.
Also, you can try heating up the D2t using a blow dryer just before application. The heat will reduce your work time, but it will make it more fluid temporarily. If I remember correctly, the addition of denatured alcohol (a couple drops) will slow the cure time.
There are folks on here with much more experience at thinning dt2 than I though.