GRE through a SonicWall

I have my own IPv4 /24 at home with a SonicWall TZ170 at the border running in bridge mode (no NAT, the upstream ISP router is .1, my SonicWall TZ170 is .2). My tunnel to HE is up, but traffic won't pass, which I suspect upon sniffing is due to GRE (protocol 41) being filtered.

My problem is that the SonicWall blocks GRE. I can't create a bypass subnet around the SonicWall in my /24 because the ISP's upstream has a /24 subnet and they won't change that and won't give me a transition network (it's DSL, so they only support this one configuration for bridged IP space).

This is as annoying as heck. I can upgrade the TZ170 to SonicOS enhanced for $400, which SonicWall _says_ will pass GRE, but the upgrade is a one-way deal. It would also turn my little home IPv6 test project into a major spouseal-approval ordeal (we have three kids in college).

No cheap TZ-170-enhanced units on eBay either.

Is there another way to transport this tunnel? UDP? GRE over UDP? I can't think of anything, but I'm not as smart as I think. So I'm checking here before I give up and shell out for an upgrade.

-mel