How do I electronically file if I have to send in Form 709 but it is not supported in TT?

[TomK]

Unfortunately, you won't be able to file a Gift Tax Return with TurboTax.  A Gift Tax return should be filed separately from your personal income tax return as it has no effect on taxation at the individual level.  

The IRS provides Form 709 and Instructions here:

Form: https://www.irs.gov/pub/irs-pdf/f709.pdf

Instructions: https://www.irs.gov/pub/irs-pdf/i709.pdf