FC5: How to run an old binary that wants non-NPTL glibc?

[Mikko Huhtala]

I'm planning to migrate a site of about two dozen desktops from FC3 to
FC5. One of the apps we use requires LD_ASSUME_KERNEL=2.4.9 on FC3. I
have been unable to run it on FC5. The LD_ASSUME_KERNEL setting, of
course, breaks everything on FC5 because the appropriate version of
glibc is not present.

The error I get is

  relocation error: [ ... ] : symbol errno, version GLIBC_2.0 not
  defined in file libc.so.6 with link time reference

apparently because 'errno' is defined differently in the NPTL-version
of glibc.

The obvious fix is to patch the source and recompile, but
unfortunately the app is Closed-Source Legacy Crap (TM) from Big
Unresponsive Company Ltd.

Any ideas? Is it possible to compile a non-NPTL binaries of glibc 2.4?
I'm willing to try any kind of ugly hacks, including but not limited
to, editing symbol tables in binaries.

Mikko