Interfacing to E&M channel in TO mode

The goal: To interface Asterisk to a channel bank equipped with 4-wire E&M cards operating in Transmit Only(TO) mode. The TO suppresses A/B bit-robbed signaling, also called Channel Associated Signaling(CAS), thus allowing call setup only in outbound direction.

The problem: We were not able to identify T1 interface signaling mode in Asterisk suitable to accommodate 4-wire E&M in TO mode. Basically, what’s needed is connecting Asterisk to “clear T1 channel”, i.e. T1 without any signaling aka. pure data. By now we have spent quite a bit of time experimenting but had no luck finding a solution. Asterisk does not seem to support this mode of T1 operation - am I correct?

Note: There is no problem connecting to a channel bank with a standard 4-wire E&M circuits supporting either immediate or wink signaling. Obvious patchy solution would be to use E&M immediate with M and E leads looped back. However, our customer does not provide wiring for E&M signaling and so using E&M channels in TO mode - without signaling - is the only option.

Any suggestion would be greatly appreciated.