I had a similar problem with this video card when I flashed it's bios with a similar one (another maker). No injector or efi string could let me change the resolution and I had some artifacts also browsing the web. Finally I flashed back the original bios and it's all right now.
What I mean is that maybe some bios (8400gs line) are the trouble, not the injector.
Anyway it's a bit risky but not impossible but you'll need to get an updated bios file for that.

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CPU: AMD Athlon 64 3000+ @2.3Ghz - Motherboard: ASUS A8N-SLI nForce4 SLI - nForceLAN by eno - SuperNForceATA by Medevil - RAM:2 GB DDR 333Mhz Audio: ALC850 Video: XFX nVidia GeForce 8400GS 256Mb (0x06e4) QE & CI from Chameleon 2 RC4Ethernet: Realtek RTL 8139 Series (working out of the box) OS: Snow Leopard 10.6.4 (aryajuanda's guide) + Windows XP 64bits