It appears to be working in TurboTax Deluxe after testing. You must enter it in the charitable section as usual and then click the "wrap up deductions and credits" for it to pick the standard deduction and apply the $300 above the line.
Once you make the entry you should be able to check it by using the Tax Tools:
To find Tools:
Sign into your TurboTax account and open or continue your return.
Select Tax Tools in the left menu.
You'll find Tools beneath Tax Tools.
Select View Tax Summary
Select Preview My 1040 (left black panel)