vsto repurpose font comboBox - vsto

Question

I'm trying to repurpose the built in font selector for my own objects in PowerPoint (vsto add-in). I repurpose regular commands (bold, italic etc.) successfully using the ribbon xml.
I have a test that looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui" onLoad="Ribbon_Load">
<ribbon>
<tabs>
<tab idMso="TabAddIns" label="Test">
<group id="MyGroup"
label="My Group">
<comboBox idMso="Font" label="ComboBox1" onChange="ChangeCallback"/>
</group>
</tab>
</tabs>
</ribbon>
</customUI>
If I have a regular is instead of the idMso this callback works fine:
ChangeCallback(Office.IRibbonControl control, string text)
{
Debug.WriteLine("Changed");
}
The callback stops working when I use idMso="Font", but the comboBox works and I can use it to select font like normal.
I have tried the following callback with no luck.
ChangeCallback(Office.IRibbonControl control, string text, ref bool cancelDefault)
{
Debug.WriteLine("Changed");
}
When I repurpose commands I put it in the commands section of the xml instead of the ribbon, but having a comboBox element there is not allowed.
Any ideas on how to get this to work?