I see two alternatives:

(1) Use fesetenv.  I don't know what the appropriate value to pass would
be though, or even whether solaris lets you use fesetenv to control the
x87 precision.  It seems that its primary purpose is to set flags and traps.

(2) Use inline assembly, assuming that suncc supports this.  This seems
simpler.  It's just a matter of figuring out the syntax that suncc
expects for asm, and making sure the code is properly tested.