I keep on forgetting how to do this so this is a note to self in terms I understand (ie pictures):
Add the related entiy object to yours (in the example we are adding RegionEO(list of values) to CountryEO)
Now add the RegionName field from the EO and a transient attribute (I named mine RegionNameLOV)
Make the transient attribute updateable and base it on the expression RegionName (the description you wish to display)
Add a list of values to RegionNameLOV and map BOTH key to parent fk (region id here) AND RegionName to your transient coulmn (RegionNameLOV).
Then just drag the lov item onto the page (RegionNameLOV)