I recently did this... yes the squeal is a natural reaction and is not a problem. You have to hold the rat firm and probably have someone else do the back legs... just snip the tips, you don't need to get much for the clipping to be effective. The fronts, well you nestle the rat in your lap and hold out the front palms and hold them firm and then do the same thing... it may be also easier to have someone do the clipping and you the holding for both backs and front. The rat will squirm, may squeal, and generally not like it... you have to take little breaks every couple snips... try to be calming to the rat and when it is over have a treat ready.
Trust me, the rat won't hate you for it... but if you are worried about bites, hold the rat with work gloves. I did this, but the rat did not bite... he actually licked me between doing the backs and fronts. Weird eh?
The rat squealed doing the fronts, but only when the snip was sideways, and I think they do this because they are anticipating something bad, like when you have to get a shot when you are a kid.
Just make sure you only snip the tips and you will be fine... no need to snip any more than just the very tips.
It sure helped the quality of out-time with my rat Tiny... he is the one that a brick did nothing for, and the nails were cutting me and snagging on everything... it just had to be done, and I am glad I did it, and am not worried about doing it again.
Oh one more thing... the rat may fear poop when you are holding him firm... this is also natural... and a good treat after the entire thing is over is the way to go... treats in between parts is not going to teach them.