That is not possible unfortunately, due to the architecture of the HamAlert matching engine, which needs to use certain optimizations to be able to match hundreds of spots per second against ten thousands of triggers. Those optimizations preclude text/substring matching.
That is unfortunate, but understand there are limitations and tradeoffs in the processing power needed to search strings.
Since I will be pulling in the telnet data at the point of use, I am playing around with a Telnet server/filtering program (CC User) that pipes in multiple Telnet sources to a single Telnet output. Maybe there are some filtering capabilities there.