A method of operating a printer repetitively merges a purge sheet into a media stream of a job stream in the printer so the controller of the printer can operate inactive inkjets and eject ink onto the purge sheet to maintain the operational status of the inactive inkjets. The purge sheet has a width that is at least the maximum width of a print zone in the printer in the cross-process direction and a length that is less than a length of any media sheet in the job stream in the process direction. The purge sheet is diverted through a duplex path in the printer to repetitively merge the purge sheet into the media stream of the job stream to maintain the operational status of the inactive inkjets.