I have used FreeTDS successfully from Linux, and I _think_ perhaps from Solaris as well (but I don't remember, that was several years ago).

One thing I learned: configure the server as using TDS 4.2 in the TDS config.

But if it's not possible, I'd just buy the ODBC driver. Consider the cost of development time and system complexity and stability of the third option... It's probably worth a bit of bureaucratic slalom. Try to make it a problem of a stakeholder inside the company :)

/J