Sorry, but there is no other way to connect the subwoofer.
I’m sure there are optical to analog converters that could get a signal to the sub, but the optical out will probably be a fixed level signal that won’t respond to the soundbar’s volume control, and probably not the TV’s remote control either.
Unfortunately, this is the kind of flexibility one gives up when opting for the convenience of a soundbar. Soundbars are typically closed systems that don’t allow add-ons like this.
Regards,
Wayne A. Pflughaupt