Sub Report relative paths

I'm using Crystal Reports 11 and have 2 reports that share a common sub report.

I have created a copy of the 2 reports and the sub report. I then edited the copied sub report and attempted to reimport the edited sub report into the 2 copied reports. However this action reimported the original sub report rather than the copied one.

How do you specify a relative path for sub reports linked to a report?

Thanks