Yes when the seller signed the listing agreement the seller agreed to pay the listing agent a certain commission amount. Also there is a section in the listing agreement that addresses paying a commission to the cooperating broker.
So yes if there is no coop broker, (you use a lawyer for instance) I do not see why you could not submit an offer to the seller similar to what I outlined in the previous post. In this case you are not represented. However you still request a credit for closing costs or adjust the asking price in a corresponding manner. Again, realize the closing cost credit is limited to what the lender will be comfortable with. Alternately ask the lawyer to craft a purchase agreement with the appropriate credit for closing costs applied.
Personally, I do not advise anyone to ask the sellers to alter any agreements for commissions they have with thier listing agents. (just my opinion) My advice to buyers is to strike the best deal they can within the parameters of things they can influence including the asking price, and commission thier realtor or fixed fee thier lawyer would/could get based on thier agreement with the lawyer/realtor that represents them.