I've just (several days age - now I'm lazing in the sun and eating scones) come along the same stretch single-handed.
Where I've not been able to pull into the offside to stop and open the bridge, Ive stopped close on the towpath side, taken the bow rope to the far rail on that side loosely, opened the bridge and then gently pulled the boat over to the opened bridge, boarded at the bow, gone past under power and either been able to stop on the offside at the other side to close the bridge or towed it shut on a stern rope (drifting, not under power) and then shut it. With the power bridges, I've so far managed to put the bows in on the offside and clamber up to operate the bridge from there and then reboard, motor through and remoor on the off-side to close.
Two bridges refused to open under muscle power - attached bow-rope and reversed them open; it worked without drama.
Micklethaite (199) confused me (someone's nicked the operating instruction panel), the road barriers are manually operated, but the actual swing is electric...