The only and easiest way I know is to Select All (ctrl-A) the clips in Montage 2, and copy and paste them at the end of Montage 1, then save Montage 1 with a new name if needed.
Make sure the markers in Montage 2 are bound to their clips first, and Full Clip Attachment is selected on the Markers tab Functions menu, so that the markers will go over in the paste. (those might be in place already so I would just try the copy/paste and see if it works as expected).