Make a computer connecting via VPN visible to computers within the network it is connecting to

OK, here's the deal:

I have a computer (specifically, a MacBook Pro) that is connected to a standard network that is then connected to the big nasty internet. Let's call it foo. It runs a web server on 8084, and so if you were on its local network you could get to this with http://foo:8084/, or http://192.168.1.2:8084/, or whatever.

From foo I can VPN into my companies intranet and see a computer on the local company network called bar (another MacBook Pro, incidentally).

Is there any way to set this up so that while foo is on the VPN bar can access http://foo:8084/ (or http://x.x.x.x:8084/, or whatever)?

(From my limited understanding of how VPNs work I have a sneaking suspicion the answer is no, but it doesn't hurt to ask…)

Edit: one more thing, I don't actually admin the network this runs on, my control extends only to the two laptops, and our admins are… well, they aren't going to change any of their settings for this.

OK, more info. The reason I'm lost is I can't get a ping going from a computer inside the network back to the computer connecting via the VPN:

Last login: Tue Apr  6 23:49:47 on ttys000
Nosy:~ stefand$ ssh scdf@bar
scdf@bar's password: 
Last login: Wed Apr  7 18:50:00 2010 from 172.20.11.70
[scdf@bar ~]$ w
 19:34:21 up 76 days, 20:29,  1 user,  load average: 1.61, 2.00, 2.84
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
scdf    pts/3    172.20.11.74     19:34    1.00s  0.02s  0.01s w
[scdf@bar ~]$ ping 172.20.11.74
PING 172.20.11.74 (172.20.11.74) 56(84) bytes of data.

--- 172.20.11.74 ping statistics ---
10 packets transmitted, 0 received, 100% packet loss, time 9000ms    

[scdf@bar ~]$

ifconfig on the VPN'd laptop confirms that IP.