While I agree it isn't something I would ever do....
At a minimum you would need to select where the new helm would be. Then figure out how to rerouted the stearing cables
to that location. Depending on the design and layout of the boat this could be trivially easy or next to impossible, it just depends. Once you do that it's simply a matter of installing the right hardware
in the right place. Some of it you could scavanage from the old wheels, but likely not all of it. Finally you would need to build covers for where the wheels were that matched the rest of the boat.
I could see this running from say $5,000 up to around $35,000 depending on how hard it is to reroute the cables
. Some boats it would just be dropping in some pulleys, on others it may take a massive redesign of the aft cockpit
At a minimum your new wheel
would provide terrible sight lines to the sails
, since any boat with twin wheels is also going to be pretty wide, and now you only have the center line one.
I guess is should also point out that if the boat has hydrolic or electric steering
(very unlikely on any boat with twin wheels) it may be far easier. Adding a new hydrolic line would be almost trivial.