http://sky.prohosting.com/oparviai/soundtouch/soundstretch.html
soundstretch mono.wav mono_ntsc.wav -rate=-4.096
Like I said, a doddle...
Actually, the resulting file was about 34ms too short due to rounding (23.976 is actually 24000/1001; I tried soundstretch with -rate=-4.0959 but the resulting wav was exactly the same). So I split the difference and added 17ms of silence to the start of the file. I think it's very unlikely that any desync will be noticeable, but I haven't got Dr M's DVD to test it with.
I'll post the AC-3 encoded file this evening.