How do I get Graphicsmagick's -output-directory option to work if I have no control over the working directory?

Question

Ok, this is somewhat special, but if I cannot find help here, where else should I look?

Unfortunately, I am forced to use gm's COM+ API, so I can not set the working directory. So the command line call to resize a batch of JPGs is:

gm mogrify -size 500x500 -scale 500x500 -output-directory scaled *.JPG

However, I am unable to get this to work with fully qualified paths:

gm mogrify -size 500x500 -scale 500x500 -output-directory c:\output c:\imput\*.JPG

Does not work. Apparently, the specified output-directory gets pushed before the input path.

Any ideas? I totally hate the Idea to use System.Diagnostics.Proccess.