Quoted from the discussion group post linked to below:
“You can use GA (Google Analytics) with GPC. I do.

The only editable parts of a GPC page are in the body section so you
can insert the GA code in any of the sections. I recommend in the
bottom section.

You have found one of the GPC bugs, it will not save HTML if there was
not something already in that section. It is easy to overcome.

1. Type anything in to the empty section you want to add the HTML to,
I use ‘x’.

2. Save the page.

3. The ‘edit html’ the section you put the ‘x’.

4. Delete the ‘x’ & paste the GA code in.

5. Save.

And this time GPC will save it. “