Since /ŋ/ only occurs finally and follows short vowels, while the semivowels /j/ and /w/ only occur initially, the only possible contrasts would be medial and none are attested. The pairs longer (one who longs) and lawyer or banger and buyer are close, but with different vowels. I can't even get this close with /w/, though if you were to describe a desire for success in crooning love songs as a "Bing-itch", that would be a minimal contrast with bewitch, but obviously that is not in any dictionary that I know of.