Or search: subjunction, supplementation
2 Syllables: SU
boiling, broiling, coining, hoisting, joining, pointing, spoiling, toiling, voicing
3 Syllables: SUU
exploiting
3 Syllables: USU
adjoining, annoying, anointing, appointing, avoiding, destroying, employing, enjoining, enjoying, rejoicing
4 Syllables: UUSU
disappointing

Found 21 words across 4 groupings. Skipped 1 excess word of a similar stem.