Is it possible to disable built-in aliases in the "Go" FAYT prompt?

You could turn off everything else under Preferences / Filtering and Sorting / Find-As-You-Type / Folders Mode and use ] instead of /, but it may not be exactly what you want. Folder Mode matches what you type against the target path rather than the alias name.

I think you could get exactly what you want using a FAYT script, though.