Hi,
Having alv list displayed at the end of alv grid is possible if you can split the screen to two areas where the top split can be used for alv grid and bottom one for alv list.
I think the best way is to use htlm_end_of_page to display the sales return data. Though you can not have alv list display, using html you can get the similar table display at end of grid display.
Hope this helps,
~Athreya