customer email and phone on purchase order

How do we add the customer's email and phone # to a drop ship purchase order?  Our vendors need to contact our customers via email or phone.

I found a thread about adding this info to packing slips, but when I follow those instructions (applied to drop ship purchase order), the vendor's info is added, not the customer's (which makes sense, I suppose).

We'd either like the customer's email and / or phone to appear as part of the ship-to, or as separate fields.

Thanks,
Don