If on a single clip, use “Clip->Video Options->Time Interpolation->Optical Flow”
If on an entire sequence, when you are exporting, at the bottom of export window, choose “Optical flow” as the Time interpolation method.
It isn’t perfect, and if you’re a pixel peeper you might notice some odd artifacts here and there, but in the normal course of most applications no one will be able to tell. Hope this helps.