asterisk users - Jul 2004 - extensions.conf variable declaration

Hi,

I'm setting up multiple asterisk servers and trying to do the classic

DIAL(IAX2/asterisk1/${EXTEN}&IAX2/asterisk2/${EXTEN}&IAX2/asterisk3/${EXTEN},15)

After googling a bit, I fell on a discussion about putting this in a 
variable so that adding additionnal servers would be easy. I can't seem to 
find the link anymore, but it went something like this:

extensions.conf:

[global]
SERVERS = IAX2/asterisk1&IAX2/asterisk2

[default]
exten => 1234,1,DIAl(${SERVERS},15)

unfortunately, I need to have the ${EXTEN} in the variable name. But that 
causes the ${EXTEN} to be evaluated at the declaration time (so it's 
empty).
I tried escaping the $ sign, but that didn't do much either.

Is there a way to include the ${EXTEN} in a variable so it is evaluated at 
"execution" time ?

Tried googling the archives, but I guess I didn't find the right 
combination of words :-(

Thanks

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