A way to do this would be as follows:

Program a ROM e.g. 1024 bytes with the values to drive a DAC. These values could be found by the mathematical equivalent of slicing a picture of a sinewave into 1024 slices. Then the frequency you ran the ROM address with would produce something very close to a sinewave at 1/1024 the input frequency at the output of the DAC. Depending on the frequency you need you may have to make some hardware means of addressing the ROM rather than directly from the uC.

Have fun,

Erik