How to revert an interlaced video forced into progressive?

[videdit]

I have an mpeg2 clip that is 59.94 progressive. However, the source is actually interlaced being forced into progressive (commonly done in new digital cable channels).

When looking at this clip frame by frame, I can tell they double the lines of the original fields to make a frame.

How can I take one frame, throw away the even lines, use it as odd field, take the next frame throw away odd lines and use it as even field... and end up with a 29.97 interlaced mpeg2 (or avi) clip, so I can make a normal DVD out of it?

I have premiere, after effects, tmpgenc..., if they can be used somehow to do this

[gadgetguy]

You should be able to do it with Avisynth using SeparateFields(), SelectEvery(), and Weave().

[manono]

AssumeTFF()
SeparateFields()
SelectEvery(4,0,3)
Weave()