How can I connect multiple wireless headphones to the same Iphone 6 at the same time?

I like to listen to audio files on my Iphone 6 while jogging outdoors.

My girlfriend wants to join me (jog with me and have her own headphones listening to the same audio).

How can we both pair our wireless headphones to my Iphone simultaneously so that we're listening to exactly the same thing?

(And these audio files are not available in some shared location like Spotify.)

(Also, we own a headphone splitter, but using wired headphones is inconvenient since cords make running difficult.)