By request at GimpTalk...
A script to take the current pattern, scale it and leave a copy in the clipboard. Gimp 2.6 lets you use the image in the clipboard as a fill pattern, so you can just use it from there
Scale is from 20% to 500% It used Lanczos scaling working a a tiled copy of the image, so if the source pattern is tileable the scaled one will be as well.
You can access the script by right clicking on a pattern and selecting "Scale Pattern..."