I've never actually done this, so please take the reply with a grain of salt. It does however seem to me, from reading the Tk documentation, that this should be possible.

http://www.tcl.tk/man/tcl8.4/TkCmd/canvas.htm#M60

-x position
Specifies the x-coordinate of the left edge of the area of the canvas that is to be printed, in canvas coordinates, not window coordinates. Defaults to the coordinate of the left edge of the window.

-y position
Specifies the y-coordinate of the top edge of the area of the canvas that is to be printed, in canvas coordinates, not window coordinates. Defaults to the coordinate of the top edge of the window.

-width size
Specifies the width of the area of the canvas to print. Defaults to the width of the canvas window.

-height size Specifies the height of the area of the canvas to print. Defaults to the height of the canvas window.

I may be wrong, but it should then be possible to divide the canvas height by some factor, resulting in a number of pages, and then adjusting the -x -y -width -height parameters and doing one ->postscript() call for each page.

YMMV. Good luck :-)