Yes, that's very much possible!
We've launched a session called Choose Your Own Soundtrack, which features a light only experience and the ability to play background music via another app or experience the app in silence.
There are multiple versions of Choose Your Own Soundtrack which you can modify the length of or even experience endlessly:
Choose Your Own Soundtrack (meditative, relaxed, intense)
Choose Your Own Soundtrack Sleep
(Also, on iOS app only you can turn the audio off on all sessions but only play background music via the phone on the Choose Your Own Soundtrack)