Here, I found what i was looking for:

[FARE] ISP-RNO/US/KJAUSJ6Y/186 USD
[ROUTING] 300 FROM-TO ISP-US-PHL-US-WAS/PHX/PHL/CLT/BOS-US-PHX-US-RNO*
[TRANSFERS] 3 TRANSFERS PERMITTED IN EACH DIRECTION.

This fare - ok it's not the cheapest for a MR - allows 4 flights per way. ISP-PHL-CLT-PHX-RNO should be possible, but I was not able to book, either on USair.com or any online booking tool...

Such a routing seems to be hard to find... Most domestic fares on US allow to transfer once or twice trough a US Hub.

United used to have a very generous routing and transfer policy. A fare JFK-LAX allowed a max of 5 flights and you've been able to fly across the US (i.ex. JFK-IAD-ORD-DFW-DEN-LAX). But with the merger with CO, this 'flexibility' has been eliminated