Try, rather than grabbing the paw (someone else mentioned it's the grabbing that freaks them out, not the actual clipping) just grabbing the base of the nail right before you clip it, OR grabbing the toe, rather than hovering over the dog and grabbing his whole leg.
Mine, over the years, have become REALLY good about having nails done, but they still will try to pull away if I grab a paw instead of an individual toe or nail...they are worse about the back legs for some reason.
Rather than going from just touching the nail to clipping, get him used to you just touching his nail, then get him used to seeing the clippers (like how most dogs freak just when SEEING a leash...same concept only with a negative reaction). Treat him for sniffing them, etc...then touch his paws (don't clip) with the clippers and treat for tolerating that. Then grab a toe with clippers in hand, treat. THEN, grab a toe and clip quick before he notices, and treat and praise like crazy. Took several goes at it and a looong time (and in the meantime, loooong nails) before my dogs got good at it, but they did eventually. I should frame a picture of my mom with Molly when Moogs was around six months...my mom had her in some freakish headlock with her back leg all twisted underneath her while clipping nails...it's friggin hilarious!
I won't pretend to be an expert, and who knows what might work on your dog vs. mine...just offering suggestions. Be sure to always treat with a high value treat, and never get frustrated...if you feel yourself getting frustrated, just quit where your at, otherwise your dog will get upset too. I made that mistake a few times with mine...I'd get frustrated and yell at them and then they'd be even more scared/nervous...no good.
Also, I don't know if this is something that evolved AFTER they got accustomed to clippings or before, but my dogs get nails clipped while laying on their sides rather than bellies or backs...and, they both have tolerated the Dremmel grinder much better than clippers. They tolerated clippers before but would still sometimes jump at the sound of a clip (I never quicked them)...none of that with the Dremmel, though they do get sick of laying there...it takes a lot longer than clipping.