1. You could have two different customer (or vendor) codes including the buyer's name. Then each buyer would use their own as the "Ship to" on the PO.
2. They could just type in their name in the Attn line of the ship-to section.
3. Create separate RTMs for each. Add whatever text you desire. Name, phone, email, etc. This would be my choice.

Fijn,
 
With Evo-Erp, you should be able to have that as it remembers the user login, whereas classic does not.

You could set yourselves up as Vendors. That way, after you enter the Vendor you are issuing the PO to, you enter yourself as a "V" fpr vendor and you can setup specific contact information for each person. That is what I did and it seems to work for us. You can set them up using a "look-up".  
 
Hope this may help.
 
Tommy