In MII 14.0 SP04 we introduced a new i5Chart display template and JS library to accommodate this so you don't have to instantiate the Viz library directly; I highlight this here:
http://scn.sap.com/community/manufacturing/mii/blog/2013/10/31/sap-mii-and-html-5-demystified
The help documentation also covers this along with the available JS functions for the new i5Chart and i5Grid display objects:
I recommend using these rather than manipulating the Viz library directly.
Hope this helps,
Sam