"Give them the choice between the racial bonus and their racial trait for both species.
They retain any lowered attributes but have to choose between racial traits and higher attributes"
I like this, but I would also add they take the starting WT, ST, and XP of the race with the lowest of the 2 of the pair. This would stop a Half Human/ Half Wookie from having 110 XP and a brawn of 4 to start with.