I may be on the wrong track here, but:
Asset host is not your application's host, asset host is a host that serves you /app/assets folder and this is configurable so you can set up a CDN for example, it's not intended for hosting action points.
If you want to target the full url of your own host use rake routes to get the route name corresponding to /plans/collapse_plans which probably looks something in the lines of plans_collapse_plans and then you can use plans_collapse_plans_url and rails will render the correct full URL for you.
If you're using the default host name rails provides automagically this will "just work", i.e.
[2] pry(#<#<Class:0x000000048fd780>>)> account_edit_url
=> "http://dev:3000/account/edit"
If this doesn't "just work", you can override all url helpers in the app by overriding default_url_options in your ApplicationController:
def default_url_options
{:host => HOST}
end
and be sure to set the HOST constant in your application's environment, for example:
[1] pry(#<#<Class:0x00000005047d10>>)> account_edit_url
=> "http://o7ms:3000/account/edit"
If you need to override this just in certain situations you can leave the ApplicationController alone and do:
[3] pry(#<#<Class:0x000000048fd780>>)> account_edit_url(host: MY_HOST_FOR_THE_OTHER_THINGY)
=> "http://foo:3000/account/edit"
In all cases you'll set up a config option in one place and all endpoints in the app will adjust.
EDIT
If you want to go fancy,
see default_url_options and rails 3,
by overriding url_options you may be able to implement pretty calls like account_edit_url(ajax_host: true), the url_options method would look something like this if this works:
def url_options
options = super
if super.delete(:ajax_host)
{host: AJAX_HOST}.merge(options)
else
options
end
end