Just for sake of completion...
- I ended up using a custom search help to:
- pull in the distribution channel within the search help exit code for the custom entity code when a sales org was selected in it.
- Only display sales organisations which were already present in MVKESALES
- I used derivation BADIs to default entries based on sales org.
- And I used the check entity to make sure no custom entity entries were allowed for sales orgs not in MVKESALES
A very round-a-bout solution to my problem but I never did find out out how to situate my custom entity under MVKESALES