You can place the related description field right next to the account code and shrink the dropdown field to just the arrow.
this will make it look like they are selecting the account by description
In the value list you can select both fields and select the display only values from second field so they dont ever see the code.
I don't know if that will work because the drop down box comes from a value list whose values come from a table that are not related to the table where the data will be stored.
Well you can establish that relationship account code in your table with account code in the value list table it seems reasonable to do so