Extended Mail Merge Fields

Extended Mail Merge Fields

Is there a way to create a template that will take mail merge information, and "reach" somewhere else for the input? 

We have a custom module that contains many fields of information for each record. The record is an object we are selling with the fields being attributes or features of the record. The fields within the record are very short, basically describing a SKU.

We would like to create a template that allows us to create a proposal of the record to send to customers. The template record ID will be the primary object that the template is using. So simply mail merging the fields within that record is easy. What we're trying to accomplish is to find a way to see that field information, and then go out and pull in a more detailed description. 

Example:
We have a record for a computer that is in stock and ready to be sold. The computer is specced with 3 different features which are described simply with SKU's within the record. So when we open the record we would see it as:

  1. Computer 123

Field Name
Selection
Hard Drive
Model A
RAM
Model A
CPU
Model B



    1. Hard Drive: Model A
    2. RAM: Model A
    3. CPU: Model B
When we put Computer 123 on a proposal we will set up our template to have a layout looking something like:


Hard Drive
 [Mail Merge extending to detailed description for Hard Drive Model A]
RAM
{Mail Merge extending to detailed description for RAM Model A}
CPU
{Mail Merge extending to detailed description for CPU Model B}


Customers will then see: 

Hard Drive
 SSD hard drive with 2 TB of storage
RAM
 16 GB of RAM
CPU
 Fast CPU (I actually know nothing about computer hardware in this example)

Note that these descriptions can be much longer than the example above. 

I had started to accomplish this by making the fields within the primary record a Lookup field. This allowed us to do what is described above by created a 2nd custom module that held those longer descriptions. The problem is there is limited lookup fields allowed and not enough for what we need.

Is there a way to use mail merge with standard fields and based on the selection of the standard field input something else (instead of the standard field contents)?