I came across the same situation. As it turns out, it is possible to print the GR slip from CO15.
The SAP Help link below specifically mentions CO15. It turns out the parameter NDR needs to be set. This is the equivalent of opening the MIGO transaction and setting the check box.
You need to set each one of the following:
- Version for the transaction under Print control -> General settings (example: version 1 for transactions CO11, CO15, MF40)
- Condition record for the output type under Output determination -> Maintain conditions (example: output type WF01: condition for transaction/event type WR, version 1, print indicator 1)
- Parameter NDR = X (capital letter!) in the user master record
- Printer determination
http://help.sap.com/saphelp_40b/helpdata/en/47/6dec6eb435d1118b3f0060b03ca329/content.htm