SevenCubed, the more important question is, does Google consider this unnatural.
You are giving them far too much credit to think that they have built an algorithm that can unravel carefully woven legitimate links.
Besides, there are many alternative search engines out there that parse it as perfectly natural, and it is. Never mind what google thinks -- they've lost their marbles.
I've used these types of technique for various sites and it works well across all search engines, yes including google.
Just forge ahead with what's best for you and your customers or close shop. Most importantly don't try to get a whole whack of backlinks suddenly. If you can get a very small amount over a year (like a dozen or two) from very high quality relevant sites things will slowly improve. But if you only want to get rich quickly overnight -- I have no suggestions to offer. The more queries your site can answer related not only to the main focus but also the underlying supporting queries the more you become an authority, the higher in rank you will climb, irregardless of what peg hole they currently have you stuffed into.
Don't overlook supporting secondary keywords. They must be built into your content and backlinks. The more local your focus the less you need to implement that. But if your reach extends to a national or international audience it becomes necessary to reach deeper into your barrel of reserves. Only implement as much as necessary until you cover your base audience. In your example -- widget sheet music, widget fingering chart, scales, history, etc... Offer those types of things as a value added perk even if you have to pay someone to produce the originals for you so you can give them away for free. The payoff comes in the form of an extended audience which will improve your chances of selling your product on a broader ground. Over time you will receive residual benefits from it in the form of sales of your primary product.
Your absolute best investment is to find someone who TRULY understands that web copy writing vs offline writing is a completely different ballgame. Both types of writers must be creative but the one writing for the web must also be scientific with an emphasis on numbers (percentages) and patterns rather than only words -- something they probably don't teach in literature classes (yet).
Sooner or later the nice men in their black suits are going to check in on the staff at the Plex to see if they have been taking their meds. When they get locked up you better have developed a site that appeals to all search engines as the playing field evens out. You should develop a site that appeals to an engine such as Bing (currently), then tweak it until google warms up to it. The architecture that Bing parses for is in general what all engines currently use as a guideline to varying degrees. Whereas google is trying to force irrational logic to mold the internet to their needs. It will fail, it's inevitable because they are bucking against the unifying underlying order that keeps chaos from winning.