Hi
I am pretty certain you can't do this in VP.
I think the nearest you could get would be to copy a frame from your Video as an image and then add the effect you require to this image in an external editor Then put the frame (image)back into the sequence with a duration of 2-3 seconds. Your video would then pause for this amount of time at that particular frame when you played it.
Obviously you could do this for many frames but you would have to experiment to see if the final effect is what you want which would be a lot of work for something which might not be too effective
Have a look at the filters for virtual dub, you may find something there.
Nat