We have been able to use the PXE menu and a script to do imaging at all of our remote sites. We have a trigger in our database that sets a preferred server entry on all clients to point them to their local server. The script references that value and the programs and files are loaded from that local server.
LANDesk can cache an image on a peer, though it is a bit outside of the box thinking and it may not be practical considering the fact that if the terminal with the cached image fails you're a bit stuck. What I've done at some sites similar to yours is to have a separate partition on all of the systems which I use to copy the latest image and drivers down to via landesk while the system is operational. Using LANDesk's targeted multicast and peer level download allows you to trickle the image over the WAN without saturating your links. Once this is done, you can create jobs to image systems from one partition to the other, which would be accessible via PXE. You can get creative and have the script identify another machine on the same subnet, map a share to it's secondary partition, and use the image and drivers on that if the entire drive goes as well. I imagine if you had a server with storage space at each retail location you would leverage those instead of trying to image from a central location.
A bit of a side question: You have at least 750 PXE representatives to service each of the retail sites? It sounds like there are some other options available to help minimize the footprint as well as some OS deployment and provisioning solutions that we at BizCarta have developed which would help you tremendously. If you'd like, I can ask one of our US consultants to contact you and tell you a bit more about it...