hostname redirect question

[qstreb <qstreb_(_at_)_ism-computer_(_dot_)_de>]

Hi misc,
I guess my question is a bit OT,
but i really need your help

The situation is bad, i am not allowed to use vpn
for the exact reason vpn is designed

small expl.:

    remote client
          |
      internet
          |
          |
     dsl /OpenBSD
            |
            | int.network
 ----------------------------------
    |      |      |      |      |
  Serv1  Serv2  Serv3  Serv4  Serv5
      tcp ports (21, 80, 10150)

The remote client should be able to connect to
these 5 servers for (http, ftp, sp.appl.)

The standard solution would be:
a vpn tunnel b/n "remote client" & "dsl /OpenBSD"

but my task is to manage it without :(

so what for solution would be possible?

the idea about port redirecting is rejected also

the "dsl /OpenBSD" uses dinamic ip,
so the only thing which comes to my poor brain is:
using dyndns I could get 5 dyndns hostnames and to
redirect hostname_1_5.dyndns.org(not ip) to Serv1_5
which involves the use of any tcp proxy/redirect appl.
(no idea about such proxy application :(

10x and greetings,
qstreb