You may want to have look at a utility called X-Mouse Controls. It allows similar behavior to what I believe you are looking for. To use it:
Download the .zip file from the link above and extract it (e.g. with 7zip).
Run X-Mouse Controls.exe (not .config).
In the dialog box presented, check just the option to Activate window tracking, then click Apply:
ex. X-Mouse Controls - Focus Follows Mouse [FFM] Settings

- Close the
X-Mouse Controls.exe window.
Hovering the mouse over a given window should now (generally) allow it to e.g. accept keyboard input, but not automatically bring it to the top of the windows stack (i.e. change its z-order).
Notes
You can still brings windows to the foreground by clicking on them.
Some keyboard input may still cause a window to come to the top of the stack (e.g. tabbing to certain window UI elements).
Enabling Activate window tracking in X-Mouse Controls.exe will be reflected in the Ease of Access Center for Windows 7 under Activate a window by hovering over it with the mouse (i.e. this option will be checked). Similarly, if Activate a window by hovering over it with the mouse is checked in the Ease of Access Center for Windows 7, both the options for Activate window tracking and Activate window raising will be marked in the X-Mouse Controls.exe dialog box.
Related Links
How do you enable focus follows mouse in Windows 10? (Super User)
How to make mouse in Windows 7 act the same as Windows XP? (Super User)