How to programatically add a C# project to a solution sub-folder

I am using VS2012 to create a customn solution via the New Project wizard.

I am programatically creating a multi project solution inside an implementation of IWizard.

In the RunStarted() method, Obtain a reference to my solution from the automationObject parameter like this (simplified snippet):

{
    DTE2 dte = automationObject as DTE2;
    Solution4 solution = dte.Solution as Solution4;
    Project subProject = solution.AddSolutionFolder("ProjectFolder");
}

I can do

solution.AddFromTemplate()

to add projects to the root level of my solution, and I can do

testProject.ProjectItems.AddFromTemplate()

to add Items to the 'ProjectFolder'.

How can I get my projects into 'ProjectFolder'?

Thanks in advance

Paresh