It seems to me like the two longest strings will still need a retainer, and the only place to put it is really close to the nut, opposite the lowest tuner? On a four-string, it goes right about where there's now a big hole, for string #5. :dontknow:
since this is really just a 4-string headstock with a 5th string added closer to the nut, it's very common to place the reatiner like you would do on a 4-string
I'm don't have access to my digital camera at the moment, else I would show you an installed image of my retainer of chioce - a Hipshot products 3-string retainer. I install it in roughly the same location as the button retainer, and it's good for the top three strings. what I like most is that the strings load from the top and can't slip out. as this image suggests, it's also a great solution for a 4-string bass
you can find these here: http://hipshotproducts.com/cart.php?m=product_detail&p=236
definitely more expensive than the standard button, but it's also about half of the weight
i dont see a reason why you couldn't put it directly next to the extra tuner. and if that is in the way when stringing up the G, i doubt it would hurt to move it up closer to tuner for the A. like halfway between the E and A tuners.
I can't seem to steal this pic, but this looks like where I'm going to go:
There's a closeup of the headstock if you click. I have a Warmoth roller retainer on my 4-string - how high is the button? i.e. the distance from the wood to the bottom of the button that holds the string? As this will be a 32" scale fretless, I am looking to maximize string tension. :headbang:
addint a string retainer will do nothing to increase tension ... given string length (bridge saddle - nut) + given string diameter + given string tension = pitch
it does increase the downward string pressure on the nut, which eliminates the potential for the string to pop out of the nut while playing. the sonic properties of an open string change slightly with the added nut pressure, but not significant enough to write a thesis on it
Fender's location for the extra string retainer is a little puzzling - they have put a screw right at the edge of the weakest part of the neck. why?? it makes more sense to locate it a little further back towards the high string tuner, but not so close that changing strings is a total pain.
the only strings in a 4+1 configuration that greatly benefit from a string retainer are the middle three. another reason to love the Hipshot 3-string retainer is that you can bring the string break angle even across the nut for all three strings