R – How to get cleartool diff to return to command line while diff viewer is still open

As described in one of the answers to SO question "Any way to use a custom diff tool with cleartool/clearcase?" I have installed WinMerge and a single diff opens fine in WinMerge based on a command of the form

cleartool diff -g filename filename@@clearcase-virtual-path-to-version-I-want-to_compare-to

But when I run that command in cygwin, it does not return to the command prompt until I exit WinMerge.

I want to execute a few such commands from a .bat file or shell script (one for each file in the change set of a given ClearCase activity) and have it either open multiple WinMerge instances, or multiple windows in a single WinMerge instance.

I was able to do that once but I've forgotten how. Can someone remind me?

I sense that this is not really a ClearCase question, but perhaps a DOS or shell question about spawning processes from the cygwin command line …