From the ssh man page

BatchMode: If set to “yes”, passphrase/password querying will be disab
+led.  This option is useful in scripts and other batch jobs where no 
+user is present to supply the password. The argument must be “yes” or
+ “no”.  The default is “no”.
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So running

ssh -o BathMode=yes user@host.with.key.exghange "command"
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Should do the business