The idea of using side-mounted slides on stub walls (1x2s were suggested) makes sense to me, and the same thing could be done with steel or aluminum angle stock.
Some slides are rated for either wall or "flat" use, with much lower weight ratings when flat.
The Extra-Heavy-Duty Slides at Lee Valley are definitely rated for flat use in the catalog, and if you follow the "tech" link on the web page you get this set of ratings:
Flat Mount 150 lb/pair
Mobile Applications 300 lb/pair
Frequent Usage 400 lb/pair
Moderate Usage 500 lb/pair
These are obviously overkill, but applying the same load ratio to lighter but similar designs might be reasonable. Note those specs show that slides subject to mobile use take a beating, for which an allowance should be made.