Basically you temporal filter the video once forwards, and once backwards, then merge the two avis together.
To do this I use two AviSynth scripts and VirtualDub:
script1.avs
AviSource("capture.avi")
Reverse()
script2.avs
AviSource("processed1.avi")
V2=AviSource("processed2.avi")
V2=Reverse(v2)
Merge(v2)
The steps you take are; open "capture.avi" in VirtualDub, apply only a temporal filter (in this case Dynamic Noise Reduction on the default (16) setting) and save the avi as huffyuv compressed "processed1.avi", then open "script1.avs" in that VirtualDub and save the avi as "processed2.avi".
Run a 2nd VirtualDub and open script2.avs, from there you have a cleaner source to work with which has been temporal smoothened but much reduced nasty side effects (notably less motion blur). Ideally you want "processed1.avi" and "processed2.avi" to be on different harddrives to avoid your harddrive being over-worked.
Tested it on a piece of captured VHS and the result is a lot better than just using one temporal smoother on forwards video. Only drawback is the sheer amount of harddrive space you need to do this with and the extra time it takes to process the source capture twice, I tried doing frame serving with two VirtualDubs so the forwards+reverse temporal smoothed videos are fed directly into an AviSynth script to avoid the intermediate avis but it didn't work, it applied temporal smoothing on forwards video only.