There is solution if you have control (or friends) on both ends of the service.
You could try to close the information loop by forwardind the used portds on the ATA from the WAN I.P. to the internal I.P. behind the router.
Only works with the first ATA behind the router.
If you have control of both ends, you could get it working with around $120.00 dollars for good.
Just get a couple of VPN routers and presto.