There are tools on the market to deal with PE parts.
One of them is called the Etch Mate, I have no idea on the price, and personally don't think I will ever have the need for one.
Some time ago when I started playing with PE parts I had the same problems.
I had no idea how too fold such small items, without squishing them into oblivion.
So I went to the local hardware store and bought my self 4 pairs of needle nose pliers, the type technicians would use.
They have no teeth, and are around 50 mm long in the snout, and around 4 mm across.
One pair I left standed, the other 3 I ground down with a bench grinder, one to 3 mm, one to 2 mm, and the last pair to around 1 mm across.
These give me the ability to fold extremely small parts, while keeping them firmly clamped.
For small right angle bends, the blade of your knife can be pressed into the 'fold' line, gently.
Hope this helps.