The best way I think would be imagining what that would look like without any banking. Heartlining means that in this case the curve kicks out as it valleys so what I think you want to attempt is to have the lead in to the turn start as the track enters the valley and bank it appropriately as it turns. You should be using the "use heart line of current coaster style" (or something = i've not got access to NL this weekend) when you set up the building method for this type of coaster - that setting will make this shaping much easier if you're not already doing it!