You could do this with the Embedded Event Manager provided your IOS is recent enough. Something like this should work:

event manager applet save_config

event cli pattern "configure terminal" sync no skip no

action 1.0 cli command "enable"

action 2.0 cli command "config t"

action 3.0 cli command "file prompt quiet"

action 4.0 cli command "end"

action 5.0 cli command "copy running tftp://10.1.1.1/router.cfg"

action 6.0 cli command "config t"

action 7.0 cli command "no file prompt quiet"

action 8.0 cli command "end"

set 9.0 set _exit_status 1

This would require you to have a file on the TFTP server with open permissions in order for the copy to succeed. This could be a security problem.