i don't understand DC-DC converter.
But if you can reference NS data sheet and APP note
it will show you how to implement 1x , 2x CURRENT PUMP.
And you can add control bit to switch current, you
can get 1x , 2x current.
In my opinion, u must have a feedback to implement the 1.5X mode. Detect the power voltage dnd use PFM control to decide if u need to charge the capacitor. This might work.