Generally speaking, you can't place an editing project-in-progress into another Premiere Elements project. However, per the FAQs to the right of this forum, you can output your final mix from one project and import it into another.
If you need to cut a work-in-progress and paste it into another project, some people have found success using a program called ClipMate.
I can't guarantee it will work flawlessly, but it often seems to do the job.
As Steve says, one cannot do what you ask for directly, but by Exporting/Sharing as DV-AVI files, one can then Import those into an existing Project. This ARTICLE will give you some background on .PREL files.
I belatedly saw this morning that you had addressed this issue in the FAQs.
I figured out last night that outputing to an .avi file and importing it
back into the other project was my only option. But thank you for your
reply and expertise.
Thanks for your reply and expertise.