If you go to the Portfolio, then in the WorkPlan, you can go to Utilities menu and there’s a “Roadmap View” button. This opens a new window for the Roadmap, and there is a Share button. This enables you to generate a “Roadmap only” widget link, which on the next window allows you to wrapper with an iFrame also.
I’ve not tried adding this to a dashboard, I think I used it in status reporting. But, hopefully that’s a good starting point for you?
Hi… to expand on Andy’s suggestion…
You could create a custom page on dashboard in which you embed the roadmap widget link and have it displayed in the dashboard under the condition that the ‘dashboard X is being opened… otherwise it would appear in any dashboard that any user created/creates.
Please be aware however it would not become part of that graph 2-column or 3-column layout, but would probably appear beneath the graph section - similar to the discussion panel.