A first transmit device (200), a relay device (202) and methods therein, for supporting wireless communication between transmit devices over a shared radio resource in a wireless network. The first transmit device (200) records (2:1B) source identities and destination identities of detected transmissions of data made by other transmit devices (204). When an own transmission of data is performed, the first transmit device (200) appends (2:2A) a report indicating the source identity and the destination identity of each detected transmission of data. By receiving (2:2B) transmissions of data with such appended reports from various transmit devices (200, 204), the relay device (202) is able to identify (2:3) two transmit devices (204A, 204B) that are not able to communicate directly with each other, and to forward (2:5) any transmission(s) (2:4) of data between the two identified transmit devices.