Define start date for each online banking account

I would really like to use the online banking functionality.
For the last 3 years i have entered all movements on my bank accounts by hand.

The problem is: if i try to enable it, it will fetch all bookings of the last 3 month on the bank account. But those are actually already present (manually entered by me). So for getting everything straight i either need to delete all my bookings manually of the last three month. Or I need to wait for 3 month without entering new transactions before I can enable the online banking. Both sound strange.

Therefor I think it is an important feature that i can specify which date for an account. With this it is possible to smoothly switch from manual to automatic.