I'm sorry but your idea simply won't work, your hole would collapse and you probably wouldn't even be able to move the pipe. Depending on soil quality. when I pound a bar through a 5' walkway.. This can be the most labor intensive part of my job and can be extremely hard.
What you could do though is since it's only 2 heasd, as you say. You don't need more then a 1/2" pipe to supply these head adequately. If The line is straight under the patio slab you could Cut the pipe as the pipe enters the, then stick a 1/2 pipe through the 1" and use the 1" as as sleeve. You May get caught up on a fitting or 2, but spend a few min and you can get them through. Stick a 1/2" Slip cap at the end of the pipe to round out the edges
What I would do first though is dig up this circular opening and confirm this is the end of the run and the pipe doesn't continue through. Also there may be a 'Tee' under the patio that continues your lateral elsewhere ( Yah never know!)
There are other ways too, such as water jetting a new line, or having a company come in and mole/ torpedo a hole for you.