Generally speaking, if it's not on the Firmware Selector, then it's not available.
However, according to the DD-WRT wiki, MX4050 is a synonym for MX4200v1, for which there is support for:
This is consistent with one other reference to MX4050 on the OpenWrt forum:
So maybe it's worth flashing as if it is an MX4200v1 and see if it works? If you attempt this, let us know how it goes and someone can update the wiki if the result is positive. If you're already using MX4050 as your main router, please switch it out for something else (or even another MX4050) and treat the MX4050 as a test bed.