orcing boxA to use gateway to get to boxB all on same sub-net...

Hi-

I'm trying to force boxA to connect to boxB on the same subnet via a
linux box configured as a gateway, yet again on the same sub-net.

boxA= 192.168.40.50
boxB= 192.168.40.110
gateway linux machine = 192.168.40.7

We used this on boxA (192.168.40.50) to add the route:

route add -host 192.168.40.110/32 gw 192.168.40.7

And we tried a non-zero metric as well.

When I try to traceroute to boxB from boxA, the first time, I can see
it pass via the gateway (machine names removed):

traceroute to (192.168.40.110), 30 hops max, 38 byte packets
1 (192.168.40.7) 0.230 ms 0.204 ms 0.234 ms
2 (192.168.40.110) 0.358 ms 0.225 ms 0.115 ms

However, subsequently, traceroute goes directly to boxB, missing out
the gateway machine.

traceroute to (192.168.40.110), 30 hops max, 38 byte packets
1 (192.168.40.110) 0.236 ms 0.204 ms 0.235 ms

The output from 'uname -a' on boxA is:
Linux boxA.blahblah.com 2.6.9-11.ELsmp #1 SMP Fri May 20 18:26:27 EDT
2005 i686 i686 i386 GNU/Linux

Before anyone suggests something like adding another network card to
the gateway and having them on separate sub-nets, I can't do that.

Thanks for any advice.