-On the CiviCRM tab, set number of contacts to two
-Change contact 2 to an organization
-Check "Existing Contact" field and "Organization Name"
-Set "Enable Relationship Fields" to yes
-Set the relationship type
-Click save
-Now you are back to the webform tab
-Click "Edit" for the existing contact 2 field
-Set it to autocomplete, set it to hide name fields
-Optionally filter by group or other filters