A workaround (but not exactly):
- Go to the page that you want to use as a homepage.
- Tap the "share" button at the bottom.
- Tap "Add to Home Screen"; give the bookmark a name, tap "add" and a new icon will appear on your device.
- Hide Safari in a folder and use your new icon instead.
Automatically added tabs will be the homepage, unless that page is already open. Unfortunately hitting the "+" still won't... I don't know if any other browsers have homepages or customizable tabs.