Look at this image of a Pratt and Whitney J58 turbo-ramjet:
63ae17a2b5962683ab44f80b9934b6d5.jpg (1180×831) (pinimg.com)
Specifically, the large tubes which bypass the compressor and turbine sections during supersonic velocities.
The thing about ramjet operation is…it only works at velocities above the speed of sound: supersonic air being “rammed” into the intake is compressed/heated by the speed of the air so it can sustain combustion.
What if we preheat these bypass tubes?
Re-channeling exhaust thrust, electric elements, nuclear, magic unicorn farts…
could artificially heating the incoming charge of air sustain a ramjet light-off lower limit at a more feasible sub-sonic velocity?