One word .. "Caverject" or as my buddies call it .. prick-a-dick
http://www.caverject.com/AboutCI.aspx
You can pop as many times as you have goo ... you can go to your own mothers funeral and hang you coat on your own dick ..
This is not for the faint of heart but there is NOTHING on earth better .. more effective and more reliable than this .. I have personally used it for shoots where I have multiple partners with multiple pops .. it takes any worry about getting staying and performing away absolutely .. More guys are using it in this biz than you would ever believe ..