I've installed the PushToWatch extension on my "testing wiki", so I can test @thiemowmde's patch. And I've found that extension no works. I've merged his patch, as behavior is same, but code looks much better.
Extension is correctly loaded and appears in the Special:Version:
Per documentation on MediaWiki.org, option should be in footer, but there isn't any option.
If someone know how-to fix this problem, it would be great. If not, we maybe should think about the option of archiving.