We did the cable re-run once on our B40 (non-Ocean) and what you describe sounds like the design of our pulpit as well.
In our case the cable was free to pull (with help of dishwashing soap as lubricant). However, I had to replace the (short-lived) light fixture only a couple of years later and found the cable to be stuck beyond pulling it away / pulling new cable with the old cable. So I ended up making a watertight joint between the lantern and pulpit.
Summary - if soap and some other lubricants (WD40?) won't help - you may end up rewiring some other route. Have you thought about trying electricians fish tape on the opposite side?
BR,
Tommi - s/y Anniina