Yeah, I mean, without redirecting your entire practice routine, I think there's only one way to learn anything–slowly and piece by piece.
I mean, I hate to be the one to tell you, but it's way less about skill, and way more about
patience and
will-power.Back in the day, I decided I wanted to be able to bust out 'that' part in "The Glass Prison."
I'm not now, nor have I ever been big on learning 'covers'–I've primarily played in 'originals' bands my whole life. That said, I've certainly cherry-picked parts/songs/solos over the years in an effort to 'up my game.'
If it's something that really moves me, it tends to stick, but other things I'd learn, play for a few months, and then promptly forget them. The solo to "Hotel California"? Yeah, I can play that right now note for note. "Eruption"? Meh, I probably only remember the tapping part.
Anyway, up until tackling TGP, I'd never really come against something that required a whole other level of playing. But, I mean, it's such a hard part JP barely can play it (especially when MP would push the tempo back in the day).
That said, I have always done tons of work with a metronome, so I did what I always do. I found a good transcription, broke the solo apart into a dozen or so parts (corresponding with the chord changes), and got to work with my metronome.
Every day, I'd begin my metronome work, and I would play through the first section, starting at, say, 100 bpm, and then work my way up to tempo (whatever it is, it's fast). Obviously, I'd have to tap out eventually, but after a couple of weeks, I had the pattern down.
There's a few different patterns in that solo, a monster sweep, and a couple of other tricks, but once I got that first few bars down, the rest came pretty quickly.
Then, after a few months, I could play along with the record, and eventually, I got pretty clean at playing it. Hell, I used to play that solo a few bpm faster than the record, just to say I could.
It was a fun parlor trick, but all these years later, I'll be damned if I can remember a single bar of that solo.
My point is, regardless of your skill level, there's a tempo you can play that unison part at. It might be at a quarter speed, but there's a tempo. Hell, I could probably play it on keyboard at a quarter speed.
So start there, and work your way up in 4 bpm increments, until you can't play it. Also, decide if you are going to sight-read it, or memorize it, because that might change your approach.
Repeat daily, and in 6-12 months you will have yourself a cool little parlor trick
My point?
If you're willing to put the blood, sweat, tears, and time in, there's probably little you can't play, especially if we're only talking about thirty seconds of music.
That all said, if you really want to up your game as a musician, simply learning a 'really' complicated unison part is probably not the best use of your time. Yes, you will build stamina and dexterity, but I've come to appreciate that there's so much more to music than shredding patterns on an instrument, and when I hear most of DT's unison work, that's kinda what it sounds like.
Best of luck–happy shredding!