Jim,
this is how I do it. I fold one of the rubber strips and cut it with scissors to make two shorter pieces. I Wrap it on the string either with waxed dental floss or serving thread so I get my string prepared first, cut to length and I fold one end into a loop. I hold the looped end of the string in my mouth, then lay the two pieces of rubber on the string of the strung bow. The bow lays across my lap. While I hold the rubber in place with one hand I take the string and lay the "loop" on the center of the rubber.
I wrap the string over the loop, loosely at first then after a couple wraps I tighten my wraps.I use 8 to 10 wraps and then stick the end of the string through the loop and draw it tight under the wrap.
Then while I hold the bow vertical between my knees I pull on the ends of the rubber horizontally and with the scissors, cut the rubber close to the end. I keep doing that until I've got a ball of rubber with the ends sticking straight out.
From there you can slide it up the string. I like to have mine about 10" from the loop.
It takes a little time to master the process but it's worth the effort.