"So here's tae the lawyer I ne'er will forgive him
For sending me up with spruce in the trees:

Given that the song is humourous, I'm wondering if an older meaning of 'sending me up' equated to modern-day 'taking the piss'. I'd then expect 'with the spruce in the trees' means trees in the forest which doesn't set up the rhyme with knees worth a spit, so it stayed as spruce in the trees.