This is from an e-mail by Sean Fulmer on Plone Users. The URL must match that of the links on the Accessibility-info page.

What you need to do is create site actions that perform the desired action. Create three new actions under portal_actions, like so:

Title:    Small Text
Id:       small-text
URL:      string:javascript:setActiveStyleSheet('Small Text',1);
Category: site_actions


Title:    Normal Text
Id:       normal-text
URL:      string:javascript:setActiveStyleSheet('',1);
Category: site_actions


Title:    Large Text
Id:       large-text
URL:      string:javascript:setActiveStyleSheet('large Text',1);
Category: site_actions

This will create the links in the site actions area. Each of these links will have a unique ID that you can use to style, using image replacement, to produce the AAA links.