I forgot to mention a few things.
The changes are in production now and used by Jenkins.
Tests by building x2goserver look successful.
The caveat of generating temporary mock files on demand by merging our custom x2go repo files with the mock base config is that every time mock is executed the root cache is being regenerated, resulting in a performance impact of about 10%. This said, build times aren't exactly deterministic and specific build time overheads may deviate from 5% to 30%.
This isn't too bad, though, and I may implement caching of generated mock config files at a later date, probably some time later in April.
Mihai