I've worked this by using port & stbd cam cleats on swivel bases mounted on the far outboard and aft corners of the cabin top. It's not Star-perfect (or even Farr 40-perfect) but it works well enough. The worst case is that you have to lean forward and grab the line initially, but if you can rest it on your knee and cleat and uncleat without having to move, that's significantly better than any setup which does not address how import that adjustment can be.
On other boats, I've mounted a single cam on swivel base on the centerline, as close to the helm as possible.
Basically, it needs to be reachable by skipper or main-trimmer or other crew without having to move from normal sailing positions when the adjustment is needed. In other words, if they have to come off the rail or squirm around or otherwise struggle to play the vang on a windy reach, the boat is rigged wrong. End of discussion.
Ditto any other critical adjustments. If the main-trimmer has to enlist the aid of other crew to make adjustments, the boat is rigged wrong. The whole process of verbalizing (adding noise to the boat,) pulling someone out of position, even something as simple as securing a beer on your weeknight fune-race, simply means the job won't get done:
when it's critically needed and
as often as it should.
I've been on enough poorly prepared boats where standard maneuvers end up being a drawn-out Sailing 101 discussion. Cruising: fine. Practice: fine. During a race: no! Which brings up another pet peeve: I can not count how many skippers and crew have thrown up massive resistance when I've suggested a day of "full crew practice."
"We know how to race!!"
<unspoken> Apparently not, otherwise it wouldn't take you five minutes to get the spinnaker up after rounding the weather mark... </unspoken>
"OK then. Call me when you want to schedule a practice. Until then..."