PC + Traktor 3 + F1 + External Headphones: Setup Advice?

Hey everyone, I'd love some advice from the experts : )

I have an F1 I bought years ago + pro headphones + Traktor 3 software.

I use a mapping for the F1 that turns it into 4 decks, and don't use a "proper" mixer.

I use the laptop soundcard.

With that said, how can I make this setup work to enable cueing in my headphones while using a USB external speaker?

I appreciate any advice - thanks!