Using jitter matrix like a pasteboard to create image

Hi. I'm trying to work out how to combine different sub-matrixes/small jitter matrixes into one large jitter matrix, but with the caveat that I would like to position them precisely inside that matrix (eg. I cannot use jit.glue for this).
I have a .png file as a backdrop, and on that image there are spaces for four frames, which will be images from a webcam which I am saving with jit.matrixset. I'm essentially looking to paste each image into a particular part of the resulting images. Does anyone have some adivce or a direction in which they can point me? I'd like to try to stay away from GL, but I'm wondering if that is necessary for layering etc.

I've looked at Tutorial 14, for positioning the matrix in a field, but I'm unsure how to combine multiple sources like this. Sorry if this is a really obvious question - I'm still learning Jitter, although quite experienced at Max/MSP.

Thanks.