Upgrade from Leopard (10.5.8) to El Capitan (10.11) without passing through Snow Leopard (10.6.8)
My understanding is that if you bring the Mac to an Apple Store they will install it for you. 
The S/L requirement is to access the store, not as a way to charge you $20. Stopping at a friends house is no different than going to the store. 

Keep in mind, moving beyond Leopard, software compatibility may be an issue. I'd research that before making the jump .