You can do two other things instead:
-Top up (as you call it) all original stakeholders who keep at least 166,666 Oras.
-Give the free shares to all current holders of Ora. I do not think those who did not own originally, but paid for their shares are less valuable, then the original owners. You can make additional modification to this to better serve your needs. (1.5 new stakes for original accounts with more than 166,666 coins and 1 new stake for new accounts with same amount or more)
The interesting here is, that people will give the dumpers now already more money, if the additional coins later depend only on the coins.
But if only holding stakeholders get additional coins current dumpers get less money for it ;-)
And mostly people who have already coins are buying in this state anyway... they should get it cheaper, if someone wants to dump...
I would top up only keeping stakeholders as KTK did that quite successfully.