I've done that plenty of times. The problem is, even though my arms are long, they aren't quite long enough (he has that problem too). You can get your hand in, but not quite the fist, at least in his case and mine. I don't think about it that much anymore though, although I think I did it some last summer. Much rather get cocksucker worship and suck huge cocks. First time I've seen this on film though. | 
