Yes, it is possible. but it is not easy. You need to write your own program to do it.  The grids allow for UDF (User Defined Functions). These functions get compiled at runtime. So you can make a grid column return just about anything you want.
 
That said. There are some examples in a file called ISUDF.SRC that do exactly this type of thing, like get the Vendor name from the bkapvend file.  That file was left out of the post by mistake, but we are putting together a patch and I will have Lynn include it.
 
To add a UDF to a grid, just type in a name when it asks for the field name for the grid (don't use the dropdown) make sure you enter the type ([A]lpha,[N]umeric,[D]ate,[I]nteger) and the length for the column. When you are done it will tell you you need to create a file called "fieldname.src" in this file is where you need to write your function.  
 
Like I said, Yes you can add your own columns but it is not easy, you need to be able to program, and be a TAS7 programmer helps too.