Bernstein suggests "Value Averaging" for a case like this. Choose a number such that you will be fully invested after a short number of years, ideally planned to include a possible crash.
As an example, this would mean saying "My stocks will rise in value $10,000 every month".
If your investments for the first month are level, you invest 10,000 of the cash. The next month, they are down and you lose 2,000 so you must invest 12,000. The 3rd month they are up 4,000 so you need only invest 6,000. The 4th month they are way up by 11,000, so you must withdraw 1,000. The 5th month they are way down by 15,000, so you will invest 25,000.
As you can see, this will likely give better results than DCA.