Im sorry mate, but Background XP can only be awarded once per character, and in Trent Lormain case, he already had his.
Seems to me that you wish to continue his story and add some more info, great! We have just the place for you to keep writing and make a jornal or "memories of" kind of thing for Trent, check out "Tales by the Fire" http://www.narfell.us/modules.php?name=Forums&file=viewforum&f=4
Looking forward to read more from Trent Lormain!
If you need more info regarding the subject in hands (note: read "matter at hand"), please do feel free to send me a PM or look for me in Narfell's channel in IRC. Take care.