I needed this solution solved in the same way the original poster expected. Therefore I created a helper function to do this for me.
function setVariable(varName, varValue, options){
options.data.root[varName] = varValue;
};
Contained within the options in the helper, is the data block, with the root of the helper variables.
I placed my variable within the root object, either assigning or overwriting with the value provided.
The helper in html looks a lot like this.
{{setVariable "thisVar" "Contents Here"}}
<div>
{{thisVar}}
</div>