It would be possible; but not simple. It would probably require writing some kind of script to do the "work" of moving files and transferring the data from one database to the other (I assume you have access to the db since you host both sites). Mapping userids from one system to the other would be a challange unless everyone had the same username as before.
Not a simple task to be sure, but one that could probably be done.
Please do not PM me for support or sales questions. Thank you for your understanding.