Yep...a bunch of folks do.
One of the helpers suggested just entering the $$ amount you are thinking of converting.....and entering that as a supposed 1099-INT, box 1 entry...(From some fictitious Bank so you remember to delete it later).
That amount is taxed the same as your converted $$ amount.
Those of us who do these estimates regularly use the desktop version of TurboTax rather than the online version. The desktop version usually allows entering Forms 1099-R in forms mode even when the section to enter them in step-by-step mode is not yet available. The desktop version also allows making multiple variations of tax returns without having to create multiple TurboTax accounts.
Entering the taxable amount of a Roth conversion as interest income works as long as you do not also enter an ordinary Roth contribution. The increase in AGI caused by adding interest income can reduce the amount of a Roth IRA contribution you are eligible to make while the increase in AGI caused by adding a Roth conversion will not.