Download the Sideview Utils app from splunkbase ( http://splunk-base.splunk.com/apps/22279/sideview-utils ), and read through its embedded documentation a little bit. You'll see there that it packages a number of new modules for the Splunk UI.
Notably, it packages a module called HTML and you can write any HTML you like into it's configuration, including <iframe> tags, and it will do $foo$ substitution while you're at it.
So in a nutshell, on the dashboard you can have a Pulldown module upstream from the HTML module. The user uses the Pulldown to select the host. This then fills in the $host$ value in your iframe's src attribute.
Then on the target view, you use a module called URLLoader to turn that ?host=XYZ into a key that will populate "$host$" values where they appear in the target view.
This is all explained in more (and better) detail in the Sideview Utils app. Read through the documentation views carefully and then focus on the 'linking' section under 'key techniques'.
