I would not recommend doing an associative link in a background sheet. Your creating a historical document and you don't want things just changing on your Drafts. Also it becomes a real pain if you want to transfer the files elswhere and if you lose the link to what ever was associated, it goes away.
Thank you Grundey for your reply but i must disagree in part. I have allways xref'd the title blocks for my projects for the past 16+ years. I do this by using two different blocks. one for the common title information and line work and a second to cover the file specific information. I have found this to be a great way to taylor the title block for customer request on multi sheet projects. For the past four years i was not aware SE could do the same until today. What a relief it is to find this option. Oh yea i also use Project specificy title blocks while doing this.
I do agree with your statment "Your creating a historical document and you don't want things just changing on your Drafts." To this you do need to be careful with the control of this Title blocks.