They can discreetly plant it on an Acolyte. Slipping it into a pocket beneath the robe would be ideal, as the Acolytes may not wear the robes outside of their interactions with the Lost. They'll be able to find an Acolyte where this is possible, as not all of the Acolytes have the same level of situational awareness.

Regardless of when the act takes place, the Spared who are attempting to track would find this doesn't alter the signal's location. This suggests the Acolytes are operating from the same area the Lost are held.

Following the escape in Part 2, those involved may wish to keep an eye on where that tracker moves to and what that information might reveal.