Well I don't mean the voucher mod itself, but the part of the code you added to it where when you use a multiple voucher it shows in the admin who all has claimed a voucher.
Couldn't that in a way be deemed as a counter to list names of everyone who has bought a certain "contest entry" from the shop?
So you would have a shop item called say "Contest Entry" and when someone buys one it list the name in a box (just as the voucher mod does) who has bought a ticket.
When the same person buys another ticket, the mod could check for previously bought tickets, and add perhaps a "x2" or "x3" etc etc beside their name.