unfortunately this isn't possible.
As option you could create a reference entity. After startup, you create for each enum. value an object. This list can be filtered and used to set the value.
There is a widget for that: https://appstore.home.mendix.com/link/app/56183/Finaps/EnumSelector
A not so great solution to this would be to use either CSS to not show the options, or to write some jquery that removes the options from the list.
Rene's solution would be the best practice.
Thanks for the replies, thought this may have been the case...will take a look at first option and give it a go.