just went to Buenaventura, but of course I did not ask for shipping. And only stayed a night, it is a port town and it was a hassle to find a hotel with parking for the bike.
Sorry I cant help you with putting the bikes on a boat, but I think it should be possible. Maybe putting the bikes on a truck, but this could be difficult because of all the border crossings and also to find a truck that goes all the way.
At the moment i am in Salento and this place is full of young backpackers that are volunteering on the farms, and they are always up for an adventure. Maybe maybe you can find two of them to ride the bikes down ... but it wont be easy.
I will ride my Africa Twin down to Bolivia in October, but thru Venezuela and Brazil.
Good luck mate
Please send me a pm if i can help you with something
Mika (a friend of your brother Dave)