Varia connection mid activity

Normally I use the following sequence in the morning when riding to work:

- switch on Edge (1040)

- switch on Varia headlight (UT800) (-> gets detected by Edge)

- switch on Varia radar (RTL515) (-> gets detected by Edge)

- start activity on Edge -> this turns on the lights as everything is in auto mode

In the evening I don't need the lights from the start of my ride, so  I want to switch them on as it gets dark.

However if I turn on the headlight and radar AFTER the activity is started, the radar and headlight isn't being detected by the Edge.

I can manually connect to the radar under the sensors menu, but there is no way to connect the light.

Any ideas?