In this scenario I believe you must have configured Vrf lite on your central site CE router.
To achieve what you need, you will have to enable standalone MPBGP so it can be done in a simple and effective way.
Once MPBGP is enabled its a matter of import and export of routes using the route targets with the aid of import-maps ( to allow only specific services like the printers routes to be imported into the guest/partner vrf;s.
Enabling MPBGP will not affect your setup in any adverse manner as its just standalone and used locally, even though you may have upstream connectivity through your CE to the MPLS cloud and this would not go into the backbone any way as well.
Also to make things more granular, you can recommend to the customer to use, different VRF's for each segment. For Eg:
1) VRF for Internal (employees)
2) VRF for Guests
3) VRF for Partners
4) VRF for Services ( Printers, specific servers etc)
This way you can lay a good foundation for future expansion and requirements.
HTH-Cheers,
Swaroop