do_sos true merely sets the values of the current energy and current correlation energy variables to the spin-component scaled values. This has no impact on the orbital optimization whatsoever. Psi4 version is irrelevant. (Use grep -inr "do_sos" . in occ if you want to check for yourself.)
The prospects for getting orbital optimized SOS-MP2 with conventional integrals are grim. The method is fairly easy, but the developer who wrote the code has lost interest in developments with the conventional integral code, and the code is so exceedingly difficult to work with that no other developers are likely to touch it.