Another solution is to insert a subroutine into @INC that checks a list of modules to fake (rather than a full filesystem approach). If the required module is in your list, the @INC sub instantiates a stub, or simply modifies %INC to fake that the module is already loaded. See require for how to do this. I remember doing it a few years ago but haven't retained that recollection. :)

I may have dived into this a bit in a Perl Conference talk in 2017: Spilling the @INC.

Update: So despite my grasping for words in the talk it does look like around 22 minutes in I begin discussing how to stick a subref into @INC that manufactures modules and a subroutine within the module (which isn't strictly necessary).