How to crack custom hash - SHA512, SHA256, and MD5 combined

I am trying to figure out how to use hashcat to crack a custom hash function. The hash I have has been hashed several hundred times in MD5, then in SHA256, etc. How could I tell Hashcat to do a custom hash function like this? I haven't seen much information about how to do this online.

By the way, each iteration uses a standard hash function with no salt.
You'd have to write your own kernel for that.
How would you suggest going about cracking something like this then? My python script is just too slow for this brute forcing, and dict. attack with the rockyou list hasn't gotten me anywhere
John the Ripper has a way to express custom hashes, but I'm not sure that it would support hundreds of them nested.

MDXfind's -i flag can be used to iterate hundreds of times, but only for a given hash type. Hundreds of one hash, followed by hundreds of another hash, wouldn't be supported directly. But you might be able to do it by cracking the first phase, and then piping the results to the second phase, etc. But this would all be CPU-only.