Yes, of course! First of all, disable instant delivery in Sendtoreader settings (on the page /user/settings/), install bookmarklet and send a page to (in your case) to sendtoreader. To download the result - .mobi file login to your account on sendtoreader.com and click "Download" link in the dropdown menu (the button with arrow on the right of each document in the "Sent recently" list.