I am presently on the process of finding a solution to my 1TB Time Capsule not having enough disk space for the incremental backups.
Since my Time Capsule allows for and external drive via USB, I connected a 2TB external drive and Time Machine immediately recognized it as an available separate volume (this means you can't spawn the first drive into the second in ordem to have a unique and bigger volume).
Too bad Time Machine can't treat each volume separately (that would allow me to, say, backup images to one volume and the Documents to the other). But since it can't, I used the external drive as a new volume (with enough capacity) to hold my Time Machine backups. I also stopped making backups on the original Time Capsule internal 1TB drive which I now use as a network drive for manual copies, backups, etc..
I suppose this thread goes back to a time where there was not the possibility of connecting an external drive, since I have not seen mention to this option - far more practical, though you end up with both drives on the Time Capsule...