I know it's not VL, but I think this is still the only true way of insuring a start of an undo group.
;++++++++++++ Set And Start An Undo Group ++++++++++++++++++++++++
(defun SetUndo ()
(and (zerop (getvar "UNDOCTL"))
(command "_.UNDO" "_ALL"))
(and (= (logand (getvar "UNDOCTL") 2) 2)
(command "_.UNDO" "_CONTROL" "_ALL"))
(and (= (logand (getvar "UNDOCTL") 8) 8)
(command "_.UNDO" "_END"))
(command "_.UNDO" "_GROUP"))
-David