Searching for a double-ESC in a command sequence is not elementary, because
termination of the command is inherent to the search string! Trying to
trick the command parser via clever use of command-line editing facilities
also does not work (feel free to try, but the parser will never read past
a double-ESC!). The only recommended method is by direct loading of the
search string in the following way:

Instead of:  @s / ESC ESC / ESC ESC       (the impossible command)

type      :  27 i 27 i .-2 , . x_ s ESC ESC
and then  :  s ESC ESC