Set Phaser 850 to default to Black and White Printing

I manage a network of 80 or so computers in a primary school. The main
printing that is used by teachers and students are two Phaser 850 printers.
These printers have performed well for three years.

Part of the deal when the printers were purchased was free black wax for
life, consequently there is a strong desire to set the printing default to
black and white rather than colour.

Previously we had windows 98 clients, and my solution of writing registry
files back to the clients on login set the default to black and white. Since
moving to Windows XP there have been a number of issues preventing this
solution being reapplied.

Currently the printers are added at logon using con2prt. Unfortunately this
sets the default to colour printing.

I would appreciate any suggestions for a simple solution to this problem.

Thanks