Certainly this is one of the most frustrating things about the in-built calendar app. I'm afraid the answer is NO.
However, two possible workarounds...
1) There are apps in the app store which support this (and are fully integrated with the in-built calendar). I use iPlan which I believe is a far better calendar app in any case (looks gorgeous and works better than Calendar), but it also allows completely custom repeats. So you can repeat 4 weekly, 7 monthly, 23 daily (?), whatever takes your fancy...
2) I think you can set 4 weekly repeats on iCal on the PC if I remember correctly. These events then just appear on your iPad (assuming you are syncing via iCloud).
There are probably some other ways too, and I'm sure our other members can chip in with their favourites...