For some time, Apple (AAPL) has been using its huge cash hoard ($117 billion as of June) as a loan facility to lock in key manufacturing suppliers. In late 2005, for example, Tim Cook signed a deal with several flash memory manufacturers worth a total of $1 billion to ensure adequate supplies of what he anticipated would be a critical component in iPods and iPhones. In 2010 Apple executed long-term agreements with three unnamed suppliers — widely assumed to be touchscreen manufacturers — through which it expected to spend about $3.9 billion in inventory component prepayments and capital expenditures over the next two years.

In his Monday note, RBC’s Daryanani focuses on the June quarter’s 24% increase year over year — to $13.6 billion — in manufacturing and component purchase commitments and its 63% increase — to $4.4 billion — in inventory prepayments.

These so-called off-balance sheet expenditures, Daryanani notes, have a high correlation to Apple’s future revenues. Basically, they are a signal that the company is ramping up something big. He takes last quarter unusually large prepayments as evidence that Apple will beat the Street’s expectations by about 10% over the next couple of quarters.

Then he goes one step further and pinpoints which contractors are likely to benefit the most from Apple’s investment in their future supplies. Of the 156 subcontractors that supply 97% of Apple’s components, he lists eighteen — among them such brand names as Intel (INTC), which supplies the Mac’s CPUs, and Taiwan-based Foxconn, which does the final assembly on most of Apple’s products.

But he highlights three relatively unknown U.S. companies whose growth seems to be particularly well correlated with Apple’s:

• Jabil (JBL), a St. Petersburg, FL-based circuit-board maker that Daryanani has identified as “an integral supplier to AAPL [that] manufactures casings and accessories for the company through its GreenPoint operations.” He estimates that Apple accounts for about 12% of Jabil’s revenues and an even higher percentage of its earnings.
• Amphenol (APH), based in Wallingford, CT, is a major manufacturer of electronic and fiber optic cables and connectors. According to Daryanani, the antennas and connectors it makes for the iPhone and iPad account for nearly 5% of its revenue.
• Molex (MOLX), based in Lisle, IL, makes connectors for the iPhone and iPad. Less than 5% of its revenue stream currently comes from Apple, but Daryanani expects that contribution to grow through 2013.

None of these three companies make components as critical or as supply constrained as flash memory or touch screens, but Daryanani seems to think they’re worth watching.