Based on an email from the CDG website webmaster, there are showers in CDG Term 2 near the RER station. But they are not attended.
Edited to add for future searches:
There is a shower room in each of the men's and women's rest rooms in the RER station next to T2. The room is about 10ftx4ft with shower and bench area. There is no attendant and no cleaning between uses so the user must bring all necessary items. The key is available from the attendant in the information booth on the same floor.

[This message has been edited by Warrenlm (edited 12-08-2002).]