Which preposition to use with optional

with Occurrences 11%

" The phrase "get supper, too," referred to the custom in the white homes of Hooker's Bend of having only two meals cooked a day, breakfast and the twelve-o'clock dinner, with a hot supper optional with the mistress.

in Occurrences 1%

" By his will Washington gave Lee his "immediate freedom or if he should prefer it (on account of the accidents which have befallen him and which have rendered him incapable of walking or of any active employment) to remain in the situation he now is, it shall be optional in him to do so

to Occurrences 1%

Vegetables are served up With the umidi, but plain boiled, leaving it optional to you to use melted butter or oil with them.

Which preposition to use with  optional