Vouchers valid on multiple m0n0walls ?

Hi,

we are going to use multiple m0n0walls to tunnel customer representatives
through our company network to the internet. To avoid abuse of the access
points we will use the captive portal with the voucher system.

I don't like the idea of managing multiple voucher lists - so I would like
to have a global set of vouchers that will be valid on all m0n0walls.

Is there a way to do this ???

Thanks in advance for any hint :)

Detlev