Question about failover on extension

Hi all, is there a way to hava a failover destination on an extension ?
In other words, if I am busy or on the phone and I have voicemail enabled it all OK; but if I have non voicemail I would like calls were routed to the operator, or to a time condition.
Also a context failover would be the best: all the extension in the from-internal context should behave in this same way.
Now I am doing this adding a line in extensions_custom.conf
and commenting out another line in extensions.conf in macro-vm
;exten => exit-FAILED,n,Hangup()

Is there a better way ?

thanks in advance,