rescale and keep interlacing

[paulc0001]

I'm trying to re-scale an interlaced image. The input is a 25 fps interlaced MPEG 2 file at 720x756 (PAL). I need to crop this down and re-size it back up to 720x576. Cropping and sizing with 'transcode{croptop=105, cropleft=65, cropright=65,width=720,height=576}' works but looks awful because of the interlacing. What I'd like it to do is:

Take a frame and split it into two fields (like the Bob deinterlace filter does for display output). Crop and scale each field. Re-combine the two fields (interlace) into one frame and encode it on the output (also MPEG-2).

Can this be done with vlc? If so, what arguments do I need to pass to the transcode module?

TIA.