Hi Erika, no, I'm afraid there currently isn't a way to do that with the back button. What I would suggest is opening the post in a new tab or window. That way you won't lose your place in the grid view.
In most browsers you can open something in a new window by right clicking the link (long press on a touch device) and then selecting "open in a new window" in the popup menu. On the Mac you can also Command-click to open a link in a new tab, and I think the equivalent is shift-click on Windows.
I know this isn't ideal and it is something that we might improve in future.
