Taking L1 and M1 as the required boundaries for a range, a formula is possible (but it did rather get out of hand - and hopefully something much simpler will turn up!):
=IFERROR(SUMPRODUCT((IF(INDIRECT(CHAR(64+MATCH(M$1,$A$1:$E$1,0))&"2:"&CHAR(64+MATCH(M$1,$A$1:$E$1,0))&"5")-INDIRECT(CHAR(64+MATCH(L$1,$A$1:$E$1,0))&"2:"&CHAR(64+MATCH(L$1,$A$1:$E$1,0))&"5")>0,INDIRECT(CHAR(64+MATCH(M$1,$A$1:$E$1,0))&"2:"&CHAR(64+MATCH(M$1,$A$1:$E$1,0))&"5")-INDIRECT(CHAR(64+MATCH(L$1,$A$1:$E$1,0))&"2:"&CHAR(64+MATCH(L$1,$A$1:$E$1,0))&"5")))),"")
in M2 and copied down to M5.