The list in the registry is something like:
HKEY_CURRENT_USER\Software\Corel\User Assistant\10\Recent Work\WordPerfect\Last Opened\x
x is letters "a" to "i". Click Start, Run, and type regedit and press Enter key. Then open one of the a-i folders. If you will notice, there is an "a" edit string and an "a" key folder. In the "a" key, there are various edit keys to describe that last opened file. Modify these and close the registry.
Unfortunately, you will have to then close and reopen wp for these to update in wp's File menu listing.
I have a macro that can automate this but it can not change wp's behavior. It can modify the registry and remove entries but wp only reflects the changes when it is reopened. The macro allows the last 10 or so files, macros and graphic files to be opened, inserted, inserted as subdoc or play for macros. If this interests you, post back and I will post it to wpuniverse.com after I tweak it a little.
There is a fairly good macro by Klaus that does most of this except updating the list like you want at wpuniverse.com's code snippet forum.