It's a tempting route, but I think it's a pipedream at the moment. I'd love you to prove me wrong, but my worry would be southwest Côte d"Ivoire (not a happy part of the world in recent years) and the border from there into Liberia. And you're right, it's not actually possible to hug the coast along this part of West Africa. It's nearly all mangroves or tidal creeks through Liberia, Sierra Leone and Guinea. In fact Ghana is the best place to do it, I mean where the road actually runs behind the beach (as in Lomé), for a part of the way. But if I was you, I'd head up through Ghana to Ouagadougou and Bobo, then cut into Mali and bike through Guinea. Guinea is the most beautiful country in West Africa. You would love it there, and people not nearly so Francophile as in Togo, Côte d'Ivoie etc. Bike through the Fouta Djalon hills, and go on the route from Pita to Télimélé - awesome scenery. Then. . .assuming today's elections have gone smoothly, you can go down to Freetown or visit the Bijagós islands off the coast of Guinea-Bissau – superb beaches and really amazing people who don't get much contact with Europeans (or mainlanders). After that, Senegal will be a snap, and probably feel a bit like getting back to Europe in comparison.
Discount flights with profits to development: www.northsouthtravel.co.uk
I am not worried about Cote D Ivoire, I am more worried about the path and the Visas.
I am in Accra, Ghana and went to both Liberia and Sierra Leone, 100 US 3 days wait for Liberia and 7 to 10 days for Sierra Leone Visa.
Not much information offered up front, more or less apply and hope.