With iSilo/X, there is currently is no way to rewrite links on-the-fly.
Another product, Sunrise supports a link rewriting feature through scripting (SDL). If you install Sunrise, you can read more about scripting under "Help Contents" from within Sunrise. There are also several example SDLs in the distribution that use link rewriting, including NY Times and Brighthand.
If you are more interested, check out our
Sunrise forum.