Injuries to Valdas Trakys and Darryl Duffy allied to leading scorer Derek Riordan sitting in the Easter Road stand suspended left Calderwood without a recognised striker on the bench.
And with Colin Nish struggling to make any impression against Saints stoppers Michael Duberry and Steven Anderson as he filled the thankless task of playing up-front alone, Calderwood turned to teenage defender David Stephens.
The former Norwich City youngster replaced Nish for the final 20 minutes and the move almost paid off as Saints goalkeeper Peter Enckelman could only push a low cross from Jonathan Grounds in his direction. But before Stephens could pounce, Danny Grainger stepped in with a telling clearance to ensure a match largely devoid of any excitement ultimately ended in a no-scoring draw.
Nish had again become the target of the terracing boo boys but, Calderwood insisted, that wasn't the sole reason he had made the change.
He said: "We were going to try to do something to add a bit of freshness, fresh legs, but we were limited because we did not have a recognised striker on the bench.
"So we put big David up there, he has a physical presence and a bit of pace when he opens his legs. So it was just something a little bit quirky; would he change the game, would he become a hero by scoring a goal?
"He had one sort of effort but I thought he did okay."
Calderwood, however, admitted his side had disappointed although he was happy enough to have avoided defeat and for a side which had conceded four goals the previous week to have kept a clean sheet.
He said: "It was a tough afternoon. But we stuck at it and the boys' mentality was good."