In theory you can build the part locally but it is a totally manual process to do so and for a large device not very practical. You can create a new part in the Parts Database created in the Expedition project and create the mapping here, BUT, and it is a big BUT, the symbol data has to be entered manually, that is all pin names and pin numbers have to be created from scratch. If you try to import the symbol into the local PDB you can only reference symbols that come from a Central Library. You could move the symbols into the library temporarily to do the import/mapping and then adjust the PDB as necessary. It would probably be easier just to export the symbols to the library and treat the part as a regular component. Better still, look at the advantages of I/O Designer for managing this process.
Thank you. I think I'll take the building the the part in the Central Library route but will also definitely look into the I/O Designer process as well.