Here is my suggestion:
Objective: create path in dashboards you want to display that lead from each dashboard to an other. This way, your user will not use the tab and do not display "ad hoc dashboard" tab during the visit.
Dashboard 1: menu
Dasboard 2 to 5: your Dashboards
On the Menu Dashboard, create links to the Dashboard you can display.
On each of the Dashboards, create a link to others and to go back to the Menu.
You may have to create dummy tab to put the ad hoc dashboard on the right side, this way, people would not be tempted to click on them.
To create a link:
1. create a simple viz that will act as a link
2. use dashboard action to make this viz, a bouton to open the other dashboard