Found this thread while looking for support myself a few days ago. As of this morning, the drivers here [RELEASE] IKEA Zigbee drivers work with the Tradfri on/off and open/close buttons.
You'll need to pair the buttons to HE, then do a firmware update (Assuming they're not on 24.4.6 already), but the FW update in HE should be working now. Once they're updated, they should report as buttons
