iPad Backup without iCloud or PC/Mac
You currently need to go either through iCloud or iTunes (PC/Mac) as per this kb article.

There are no other solutions that would allow you to do backups of the iPad.

Sorry.

I would strongly recommend you leave a feature request on the feedback page of the iPad and on the Time Capsule page. Apple read them and when they get enough request for a feature they get more incentive to implement it.