I know of a company that did the opposite to handle 2:3 pulldown for rotoscoping. They had a photoshop action that would select every other line, copy&paste to a new doc, collapse the empty space, and then paint the frame. Then, do that a second time for the other half. Finally, more actions to recombine.
I couldn't make this up. My jaw just hit the floor when it was explained to me the first time. I still shake my head typing it up to post here.
They solved the problem by increasing the work unnecessarily. So to explain the issue with more detail and not requiring peeps to jump to wikipedia, 2:3 pulldown is how 24fps film was converted to 29.97 fps interlaced video. This increases the number of frames roughly 20%, but it does this by repeating fields of the original progressive data. When you step through this 29.97 video frame-by-frame, you will see a repeating pattern of 3 progressive frames followed by 2 interlaced frames. To do this asinine made up workflow, they then increased the number of frames again. Instead, they should have done an inverse telecine (IVTC), which reverses the 2:3 pulldown returning 24 fps progressive frames. When rotoscoping, you definitely do not want to be creating additional frames "just because". Applying a small amount of logic should have suggested that these interlaced frames are odd since the orgininal source had nothing but clean progressive frames. If this was introduced in the conversion to video, surely it can be undone.
They, as you, decided it was acceptable to do whatever needed to be done at whatever expense rather than taking 10 minutes to find the proper workflow which would have saved them money. A simple phone call to the company they used to transfer the film to video would have been able to explain to them how to do this in less than 5 minutes. I know because I worked for the company doing the film transfer and had helped several other clients with the video for film post workflows. Today, it's even easier because there's like a bazillion write ups on how to do this posted on the web.
Edit: I didn't answer the question directly after pontificating. IVTC is the process that needed to be applied. Many many tools exist(ed) for this. The tools at this company's disposal would have been After Effects, Avid, etc. Later more tools became available like AVISynth, FFMPEG, and other dedicated tools were created by people to tackle this directly.
I couldn't make this up. My jaw just hit the floor when it was explained to me the first time. I still shake my head typing it up to post here.