Hi Prasad,
Thanks to TW for getting it to a stage where the process becoming more clear from being muddy initially.
What we now know is that the GL Accounts you are mentioning are derived from the PR> PO > MIRO Process.
I am not having SAP System with me currently + My ignorance of T Codes 
[ never comfortable with T Codes being a Customizing Menu Path Guy ] led some of us on a wild goose chase literally 
. Apologies all, I am guilty of aggravating this chase. Anyways, as TW mentions this issue might need a look from MM and FI point of view for sure.
If you are interested to explain further, I have some further questions [ which I am trying to make them as logical as possible using my limited SD, MM & FI understanding ] at this stage :
1) Are you using the same Material Number that you use in PO process in the Debit Memo too ?
2) Are you using Multiple unique Materials separately to represent the scenarios of Dealer Training / Dealer Development, Etc. ?
3) What are the precise GL Account Types for these - P&L / Balance Sheet Account ? Based on this distinction, we can say we can potentially map them or not ;
4) Let us say, somehow we are able to map the GL Accounts in SD, the reality is that these trying to use them in Debit Memo these will be treated as Revenue due from the Customer ? Is that what you really want ? This is a question for the FI Folks. We are just trying to recover the cost which is different than making a revenue;
5) Are you using the same Material Number in PR > PO and in Debit Memo ? That way it is Apples to Apples comparison ?;
6) Taking inputs from Point # 5) you have to also make sure that there is a reference between the PO and Debit Memo for reporting and reconciliation of amounts;
7) Last but not the least, are you really doing this Debit Memo SD Process today, but finding difficulties in hitting the right GL Accounts OR You are thinking of the Debit Memo Process. There is a huge difference here.
If you look at these questions closely and answer them each in detail you might be making a good case for your requirements. Dont go for a spin, based on the wish list of business wanting some goofy solutions but have a realistic understanding on what is needed from the system point of view.
To me, this seems way more complicated than what the initial impression was and as TW has pointed out, this needs involvement of MM & FI Folks. We cannot over simplify this requirement ?
You might even want to relook at the whole process mapping here.
Your choice ! My two cents !
Thanks.