preview content with personalization

I am looking to create a content preview dynamic javascript page similar to the "preview"-tab in the delivery template dialog; that is like but not as - the normal mirror page for a delivery - as it is used on a content. Before a delivery is created. I come up with:

document.write(ncm.publishing.TransformFromId('my:content','HTML',my:content|123')[1]);

which renders the peronalisation data (in <% brackets %>) and I guess somehow this can be used with an userId and transformed again to see the final render? I am a bit lost. Any help is greatly appreciated.