I just use my fingers. Wind a bunch of wraps then pull on it so it tightens up the coil then pinch it tight again and repeat as many times as it takes.
The factory new spring retainer is a piece of steel shaped like a C which keeps it tight in a package and makes then easy to install. You can make one out of a 1/8" sliver of 2 inch pipe. I think even PVC pipe would work.
Wind the spring by hand, then let it uncoil into the C shaped retainer. That way it can easily be placed into the recoil housing. Then the retainer is removed while holding the spring down in the housing with your thumb. Let it uncoil slowly in the housing until it's tight