I think sgminer supports solo mining just fine, it's usually more about the wallet than about the miner (some wallets don't allow solo mining). Not sure about BWK, just run it with "server=1" in the config and see whether it accepts your miners. I'm not going to say how "it's not feasible to solomine" cause it obviously depends on the total hashrate available to you. I am going to say though that mining NIST5 with amd cards is a waste of hashpower, it's kinda like mining ETH with GTX 1080 / 1080 Ti cards. AMD's are no good for NIST5, nvidia cards are much better at this algo. If you want to get BWK, mine the proper algos with your AMD cards (the ones they're good at like ETN/Cryptonight) and then exchange those coins for BWK — you'll get a lot more of them this way.