Hi.
With 1/4" it's possible, with a Speakon, not so much.
The reason is that You want to cut the speaker from the amp circuit and
AFAIK, that's impossible with current Speakon jacks.
Shouldn't cost too much, a jack plate of some sort, the jack, and some wire, possibly a bit of routing for the jack plate.
Feasible/reasonable, You'll be the judge.
I'd personally run the two rigs parallell if I was sure that the outputs are in phase.
Regards
Sam