that's right, i'm not asking about taking interlaced footage to progressive, but the other way around. i have to deliver a commercial spot for broadcast and the specs i just received require that the HD footage be:
Progressive/59.94fps/1280x720 OR interlaced/29.97fps/1920x1080. of course, it also says to export in the frame rate and resolution i shot in, but the spot is a mix of 1920x1080 and 1440x1080 (the latter shot 30f on my XH-A1, the former shot 30p on 7D). i edited in prores on a 1920x1080 timeline. i suspect that my best bet here, since i do not have after effects to create a 59.94 frame rate, is to create interlaced rather than down convert to 1280x720. of course i do the latter all the time for youtube, but i have never tried to create interlaced footage out of progressive. any advice would be appreciated!

In the past, i've output a reference and setup compressor to generate the 1080i for me. All was well.
Good Luck.

Creating Interlaced footage out of progressive is simple. You either export a progressive Quicktime, and setup compressor or any other encoding program to output interlaced with the correct field order (upper/odd/top for HD footage) or you simply turn on interlacing on your sequence settings and render out the timeline, then save a same as sequence settings quicktime.