You can change the optimized modes to any arbitrary resolution with the advanced timing tweaker. LineX2 320×240 optimized uses 2x duplication to output 640×480. You can set H.samplerate to 341 and H.active to 256 for 512×480. Or to capture 512×240 hi-res games use H.samplerate 682 and H.active 512 for 1024×480.
384p and 480p also use pixel duplication if you set 480pX2 and Upsample2x to off and you can change that to any resolution as well.