You can't make O42, but you can combine O48 and O36 to get a similar footprint. I use this on my Christmas layout.
1 - full O48 to 1 - 1/2 O48 to 2 - full O36 to 1 - 1/2 O48 to 1 full O48. Makes 180 degrees.
To do what you want, you will probably want to intermix the O48 and O36 so that there is not 2 O36 curves connected to each other but it is absolutely doable.
Tony