AviDemux, ffmpeg, Solveig Splitter.. All these tools (free and commercial) can trim your files w/o rendering. Google for Vegasaur Smart Trim, if you want to cut files directly in Vegas.
Adobe After Effects is much better for such effects. In Sony Vegas you have to create keyframes manually.
There is a helper tool (tweener), but it’s not free…
Steve,
Veggie Toolkit is discontinued (according to their website).
So, you have 2 options:
1) Vegas Production Assistant (which Magix also acquired)
2) Vegasaur Toolkit (see Transcoder – multiple .veg files and effects are also supported)
1. Place 2 clips on a track (normal and reversed)
2. Select both events and copy them to the clipboard (Ctrl+C)
3. Place cursor to the end and run Edit > Paste Repeat