Brute-force solution:
code:
use '*' /selete /persistent
if ingroup('group A')
  use x: '\\server\share'
endif
; and so on
Define designated drive letters for shares based on user groups. Readjust the ACLs on the server accordingly and tell users that the server move necessitated a slight redesign.

You could even define the mappings in a .INI file for easier modifications.
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