There is a shell command you can use to force verification of a game:
steam://validate/<id> (replace with the id number of the game)
According to valve, this will open steam if it is not running. If this works (not tested) it is a simple matter of making a batch file (plain text file named with
.bat extension) such as:
(call asks the batch file to delay execution of the next command until control is returned from the first command).
Try it with only one game and see if and when control is returned to the batch file to ensure the cmd box doesn't sit there forever waiting for control to be returned.
A quick way under (windows 7 at least) to get the app id numbers of everything installed is to go into the steam folders and find the user setting folder (\userdata\), then select all the app id folders, hold the shift key and right+click, then pick "copy as path". Paste this into a text file and then find+replace the path with