Have just installed the nifty Theme Switch and Preview Plugin by nkuttler.
You can see it in operation on the HeatMap Theme demo site.
You can now view the different Heatmap child themes by selecting from the drop down menu on the right.
Only problem at present seems to be that the widget has no title and no option to set it.
I have dropped a line to the author hopefully he can point me in the right direction.
The author as released an update so you can now set the widget title within the Theme Switcher options