Yeah, a little searching on my part and I installed the filter.
Unfortunately, the filter only worked once, and then it says that it's 'unable to load the requested plugin filter. The plugin may not be installed properly or may be missing files.'
I set up a test image with 3 layers, one of them white and it worked like a champ. The layer beneath shown through. When I tried it on my void.bmp however I got the dreaded message above. Now it won't even work on my test image. I've reinstalled to no avail.
I'm stumped again!