This is in 8.5 Advanced (XP).

I have a table called Parts and a table called Products.
Multiple Parts = one Product

The Product table has a portal where the user selects each part being
used in that Product by choosing the value from a drop down list of Part
Numbers. (like an invoice in an sales/inventory solution)

What I want to do is set it up so that when a user chooses a Part Number
in the portal's drop down list, the system will immediately filter out
that Part Number from the list. So when the user clicks the drop down
list in the next portal row, already chosen Part Numbers (from any
record) won't be available.

So if you have Part Numbers 01, 02, 03, and 04, and the user chooses
Part Number 04 in the first row of the Products portal, then clicks into
the second row of the Products portal, the list will contain 01, 02, 03,
and 05.

I can set it up to update the value list through a script, but the Parts
table could end up holding thousands of records, so updating the value
list through a script could become a little time-consuming for the user.
Anyone know of a way to update the list as described without scripting?

Thanks for any input.