hello there Mr Myth,
If you would like to purchase more storage for a differnet AppleID, that AppleID has to be signed into iCloud in Settings>iCloud. Then, this article outlines how to upgrade storage for that signed in AppleID iCloud: Storage upgrades and downgrades found here http://support.apple.com/kb/HT4874.
iOS 5 or later
- Tap Settings > iCloud > Storage & Backup > Change Storage Plan.
- Select the amount of storage you want, then tap Buy (in the upper-right corner).
- Follow the instructions that appear.
All the very best,