Just exactly how would you flash the Gapps.zip without a custom recovery. Flashing them is the only way to ensure they will work properly as a system app.
You could extract the contents of the Gapps.zip then install the apps, then use Link2SD to convert to a system app, but you need to make sure you put all the other files from the zip in their appropriate system folders as well.
Seem like a lot of work, for not a whole lot of apps.