TKOF FROM WRONG RWY WHEN EXPEDITING DEPS AT CMI.

Narrative

FOR THE SOLE PURPOSE OF BLDG FLT TIME; I FLEW VFR FROM SPEEDWAY (35Y) TO CHAMPAIGN (CMI) AND RETURN. THE FLT OVER WAS UNEVENTFUL. I CONTACTED STAGE III TRSA ABOUT 25 MI OUT AND LANDED ON 4L. I THEN REQUESTED TO TAXI FOR IMMEDIATE DEP. I WAS INSTRUCTED TO BACK TAXI ON THE 4R TO 4L AND CALL TWR WHEN READY TO DEPART. I TAXIED TO POINT A (SEE GRAPH) AND WENT THROUGH MY PRETKOF CHKLIST. WITH THE CHKLIST DONE I TUNED IN THE TWR. THE TWR WAS TALKING TO A PLANE ON A RIGHT BASE FOR 4L FOR A TOUCH AND GO. I VISUALLY SPOTTED THE ACFT IN WHAT I THOUGHT WAS A TIGHTER THAN NORMAL BASE LEG. I CONTACTED TWR FULLY EXPECTING THEY (ATC) WOULD HAVE ME WAIT UNTIL THE PLANE ON BASE HAD COMPLETED ITS TOUCH AND GO. TO MY SURPRISE THEY ISSUED ME ON AN IMMEDIATE NO DELAY DEP. IN MY HASTE TO HELP OUT THE TWR; I MISTAKENLY TOOK OFF FROM RWY 36. I REALIZED MY MISTAKE AT ABOUT ROTATION WHEN THE TWR ISSUED A HELI A TFC ALERT FOR TFC DEPARTING 36. THIS MISTAKE OCCURRED DUE TO ME ACCEPTING A HURRIED UP CLRNC AND NOT TAKING THE TIME TO RESET MY D/G PRIOR TO TKOF. THIS HABITUAL PRACTICE WOULD HAVE AROUSED MY SUSPICIONS SINCE I WOULD HAVE HAD TO RESET MY GYRO AROUND 40 DEGS.