Keeping Fields in Mail Merge

Hi Guys, 

New to the site so hi!

I am currently out of ideas on the following problem.

I have a spreadsheet with around 550 records in it which are subject to a fairly regular update from a client. I need to create a word document for each of these records that will be stored on SharePoint so that we can input our own information.

I have already created a reference document on the network so that references to the main spreadsheet so the mailmerge field to an HTTP document is not required.

So far I have managed to mail merge these records and split them into the required word documents using the add on from Graham Mayor (merge and split), however this replaces the fields with actual text following merging and splitting. Its driving me crazy. 

Im not sure even if this is possible without doing manually (could take weeks), or if there is a way to make VBA do the same job as the mail merge but keep the fields. I am trying to merge around 12-13 fields.

Thanks

Liam