The Sideview Utils docs have an example for how to do this.
In the Sideview system you just make the field syntax in stats/chart/timechart be itself a variable set from upstream. You can use a Sideview Checkbox module or a Pulldown or any core UI module to supply the dynamic arguments.
And then you plug that value in just as $selectedStatistics$.
The example is in the embedded docs within Utils, under "Module Documentation > Pulldown > static config".
Download Sideview Utils 1.3 from splunkbase, or the cooler but slightly less free 2.0 version from the Sideview site.
In Splunk core UI, it's similar except that you would need to pass it all through the world of intentions, and use the ConvertToIntention module to create a 'stringreplace' intention. There's one example of a stringreplace intention in the ui_examples app, in addition to the Splunk documentation.
