The most "graceful solution" for ACA Redux, would be to keep the same form factor and the same Hedgehog heatsink, but incorporate anti-thump protection in the circuit itself. Which means laying out a new board with new components and a new circuit for thumpus-minimus , yet still fitting to the same ACA Redux heatsink.
Fortunately this is quite possible. The version-zero ACA Redux was 120mm in diameter, and there was enough empty space on that PCB, for diyAudio members to add a two stage SMPS filter (RLRC - RLRC) with eight new components, and still fit on a 120mm PCB on the same heatsink. Today's version-one ACA Redux is now 140mm in diameter without the SMPS filter; surely the bigger board (with 36% more area) will have plenty of room for enterprising hobbyists to do a re-layout which incorporates anti-thump protection circuitry.
The only potential fly in the ointment might be component height: since the PCB is mounted upside down, all electronic components need to be less tall than the ACA Redux's support legs. This might be an issue with some electromechanical relays, so you may have to either search for shortie-boy relays, or lay them over on their side, or implement a non-relay circuit solution.
Edit: remember that it is totally up to you, how many ohms you put in parallel with the 4 ohm loudspeaker during thump-mitigation. If you decide to put 1.0 ohms in parallel with the 4 ohm loudspeaker, then the speaker gets (1/5th) of the total thump current, and the 1 ohm resistor gets (4/5ths) of the total thump current. Thump power delivered to the loudspeaker is (1/5)^2 = (1/25) as large as the no-thump-preventer original circuit. Different values of this resistor will of course give different attenuations; AND they will also give different values of peak current through the relay contacts -- which you may or may not find significant when hunting shortie boy relays.