You could draw the imageData to a new canvas, scale the original canvas and then draw the new canvas to the original canvas.
Something like this should work:
var imageData = context.getImageData(0, 0, 100, 100);
var newCanvas = $("<canvas>")
.attr("width", imageData.width)
.attr("height", imageData.height)[0];
newCanvas.getContext("2d").putImageData(imageData, 0, 0);
context.scale(1.5, 1.5);
context.drawImage(newCanvas, 0, 0);
Here's a functioning demo http://jsfiddle.net/Hm2xq/2/.
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