One strategy is setup a custom webportal for multiple workbooks and multiple dashboards.
To my best knowledge, there currently is no other workaround this.
Advantage: All 4 dashboards will load simultaneously when the webportal is accessed, 3 will be loading behind the scene.
Create a (sheet-picture) buttons in your dashboards to navigate from one dashboard to another.
I use this strategy as last resort on a very, very limited basis.
This is my rapid short response, I'll try to follow up with more pictures and screenshots later on for illustrations.