Dialplan help

hey everyone

I currently have two phones lines coming into my asterisk system, this is in a business and well one of the lines is residential line that needs to be answered by a human not my asterisk spiel. So what i currently have is when somebody calls the res line, asterisk answers, sets caller ID to hello, and rings the phones i want.
What i would like is asterisk to answer, set caller id to “hello”, wait for say 2 seconds, in those two seconds you can enter an extension (not prompted, you must know this) if nothing happens in those two seconds ring the two phones i have set.
this allows people access to the system without having to bug the receptionist to transfer the call, or after hours if the other line is busy (it happens).

anybody have any ideas how i would do this. I’ve tried using wait, but no DTMF tones are accepted during this time.
one idea i had was making a two second sound file of nothing and using background, however if i ever want to change the length i need to go through the sound file and its just ugly.

any ideas would be greatly appreciated.

Thanks
-Eric

exten => s,1,Answer
exten => s,n,Set(CALLERID(name)=hello)
exten => s,n,WaitExten(2)
exten => s,n,Dial(Sip/recept1&Sip/recept2)