VBA - Office97 - Excel

I have a routine which populates a worksheet with shapes (rectangles). Each
is uniquely identified with an index number appended to its name. At he same
time, the "onaction" property in set to call a common subroutine.

This subroutine needs to know which shape was clicked, but the calling
routine (i.e. the onaction statement) does not seem to support arguments.
Does anybody know how I can identify the shape in the target subroutine after
the action is triggered.

Please note that it is impractical to call a different subroutine for every
shape on the sheet - there are too many of them!

Any assistance would be appreciated.