I got a modification to premake put together today that lets it generate makefiles for Wii Homebrew projects.
Here are the changes to the Premake source. I used the latest rev in the stable repo.
http://pastebin.com/zFaeBiXx
Here is a sample script (Nothing too exciting):
http://pastebin.com/Kdgxcb3h
The next thing I hope to add is support for NMake Visual Studio projects.

Awesome. Can you do me a favor, if it isn't too much trouble, and log this in the patch tracker? Makes it so much easier when we can track everything in one place. You can just link back to this forum post. Thanks!
Cool, I put it on there and linked back. I also attached another diff to apply after the first one that fixes some issues I was having with linking, see my comment for details.
https://sourceforge.net/tracker/index.php?func=detail&aid=3021550&group_...
~Pathogen David
Can I suggest that a platform named 'Wii' should probably be reserved for the official Nintendo development environment, which might be set up to use the Nintendo GCC toolchain, and/or the SNSystems visual studio integration (like the PS3)
'Homebrew' platforms should probably have a slightly more specific naming convention, and should probably be shared between all common homebrew toolchains, which will inevitably be requested or implemented.
Popular homebrew toolchains that exist include:
pspdev, ps2dev, ps3dev, DevkitPPC (wii and gamecube), DevkitNDS (nintendo DS), dreamcast (sh4 based cross compilers), etc...
These gcc based toolchains can presumably ALL be setup the same way as this wii patch, and it would be terribly nice to include support for all of them (since I for one use most of them myself)...
I feel a naming convention would be very sensible here, with official platform names reserved for the official sdk's.
One other thing that WOULD be nice though, is the concept of 'platform' (currently limited to windows, linux, solaris, macosx) being extended to game console platforms, and being applicable irrespective of the devkit in use, weather it be the official SDK, or the homebrew SDK, the 'psp' platform should available in either case... likewise for other consoles.
Sorry, where I said 'platform' in the last paragraph, I should have said 'operating system'...
A long time coming—this patch is now in premake-stable.
Even though I feel bad for ressurecting an old thread, I was just wondering if any progress had been made on the nmake front. I'm looking to try and use devkitPSP and having it run through Visual Studio would be beneficial.
I have not looked at nmake, no. I don't know if anyone else has taken a crack at it.
I'll try to do it (but not right now).
My plan is to implement a sort of 'Makefile writer" interface (like XmlWriter), providing abstraction layer on top of different makefile formats.
All makefile formats have a lot of common in their syntax. Part of syntax is shared: rules and recursively expanded variables are the same. Additional non-shared functionality is also similar: includes (e.g., "include" in GNU Make, ".include" in BSD Make, "!include" in Nmake), conditions (ifeq(a,b), .if, !if), and so on). Ninja is a bit different, but also shares large part of functionality. Common API will allow to share significant part of code between different make generators, and having such this as variable scope (global vs project local) will allow to generate non-recursive makefile projects, built on includes instead of recursive make calls.
No worries, I'm just weighing up different meta-project systems. I would suggest that I would have a look at it myself, but I'm not familiar enough with lua, nor the premake system yet, nor do I think I have the time right now :(
Well, the devkitPSP work is only a small sub-project, so I'll continue using premake for now, maybe when I have spent a bit of time with it, I might be able to contribute.