RemoveLookup remove --All-- option

Hi there!

I want to select which options our users can choose when looking up opportunities.

Primarily, they should only be able to see their own opportunites with the exception of 2 users that should be able to see all opportunities, regardless of who is assigned to them.

I used the RemoveLookup option to remove the IDs of other users inside the user filter field. However there is an option --All-- which does not have a value and therefore can't be removed using the RemoveLookup("ID") function. Is there any way to remove this option, too? Or is there any way to remove all lookup options except for one with a certain value?

I'm sure there is a way this could be achived using Security options but I'm absolutely not well versed in that regard and if I could do it with RemoveLookup it would be enough for our purposes.

Kind regards

Norman