Well you could simply cycle through the facets, and write each one out to your STL file. A bit tedious, but I'm sure this would work, if you can't find any other way. STL text is easy to write.
Below find some VB.NET code to export facets into a binary STL file.
Production: NX10.0.3, VERICUT 8.0, FBM, MRL 3.1.4 | TcUA 10.1 MP7 Patch 0 (10.1.7.0) | TcVis 10.1
Development: VB.NET, Tcl/Tk Testing: NX12.0
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