Ah, think you might have a bit of a problem with this one. Forstner bits are used mainly because they bore flat bottomed holes. They present two large flat cutting edges to the wood and require considerable power to drive them, probably beyond the capabilities of a brace and bit. I know there will be people out there that have accomplished this but can you imagine having to bore 25 decent sized holes with a brace and a forstner bit?
Drill bits that are made to be used in a brace have a snail thread on the tip that actively pulls the bit through the wood, it also helps keep the hole straight and they drill a flat bottomed hole too
I would personally seek out the proper bits in the sizes you need. Google “sharpening brace bits” and there’s loads of resources that will keep your drill bits sharp and cutting for many years and there are some pretty substantial sized bits lurking in the back of some dusty workshops that might be bought pretty cheaply compared to their modern counterparts