Hi Tracey,
This feature just like the property is missing in BPC 10.
The only way to get a custom list of members in your report/input form is select the member and the relationship and moved it to selected member region in "EPM - Member Selector" window.
You may, however, choose the following in the Selection Relationship section of "EPM - Member Selector" window.
All Members - to get all the members of the dimension.
Base Level - to get all base level members of the dimension.
Once you have the list you may select the members you do not need and click "Exclude" from EPM menu.
Regards,
Kalyan.