For permissioned blockchains with the default settings, MultiChain only tokenistically uses the bitcoin-style proof-of-work mechanism, to ensure that block hashes have a couple of leading zeroes. There's no security value to this but we find that it helps developers tell the difference between block and transaction hashes!
For blockchains with permissionless mining, proof-of-work can still be used as the mechanism of securing the blockchain, so it's still fully supported by the code base.
If you want to fix the nonce for blocks, you'll have to tinker with the source code to enter your desired value, and to ensure that block hashes don't need any leading zeroes at all. I'm afraid we can't provide more detail than that.