sc.ini is going to get overwritten when you upgrade DMD so changing it is a bad idea. An alternative is to copy sc.ini to your projects local directory, this way DMD will use that one instead of its own. But this is all working around the issue that you should be passing import directories via a build script, makefile, or some type of build system (that's a bit difficult given the current state of build tools..), and not hardcoding paths to a global config file.
Btw, there are some notes on how to use DMD/Optlink and static libs here: http://prowiki.org/wiki4d/wiki.cgi?D__Tutorial/CompilingLinkingD I can't tell if it's any good until someone bothers to try things out and see if things work like the page describes. If something's wrong or that page doesn't explain what you need to know, let me know and I'll try to update it with more information.
