In have built a couple of mda library files which I am then referencing from my main Access application (i.e. using Tools -> References from within the IDE).
Is ther
You can add VBA references through VBA itself.
Dim sFilename As String
sFilename = CurrentProject.Path & "\" & whatever.mda
Application.References.AddFromFile sFilename
Just put that in your AutoExec and that reference ought to be available for everything. Of course, you'll have to check if the reference already exists before adding it, otherwise you get an error. But that's just a matter of looping through Application.References.