Yes you can add G/L Description but through modification only. Please Follow these steps to add G/L Text Field
1. Enhance CI Include CI_COBL add G/L text field to it. It will enhance ISCJ_E_POSTINGS structure.
2. Now modify control FTCJ_E_POSTINGS. you have write a logic to add G/L text to it.
Create an implementation for BADI definition CJ_DOCUMENT in SE19.
Use parameters C_ITCJ_SPLIT_POSTINGS in method CHANGE ...
For this you need to go to structure ISCJ_POSTINGS and look for CI include CI_COBL ..and add the field GL description to it....
in the BADI implmentation Write a select query to fill the description field and activate the BADI...