Hi Scott,
It's my mistake. I thought you wanted to display all the sales orgs.
Anyways, for this case, I think you can go with the following solution :
1. In user exit EXIT_SAPLMGMU_001, you will get the values of material number and sales organization which user has entered on screen.
2. Create a custom event(ZSALES) with a parameter (IM_VKORG) in the subtype business object(ZBUS1006).
3. Now call function module to trigger this custom event inside the exit and pass the value of sales org in INPUT_CONTAINER table.
This way you should be able to receive value of sales org inside workflow.
Don't forget to change the basic settings of workflow. There you need to specify your custom business object and custom event(ZBUS1006-ZSALES) as the start event instead of BUS1001006-CREATE.
Regards,
Richa