You buy a serpentine belt tool. Mine cost a little more than $30. You don't put it on the 19mm aluminum boss, you put it on the 15mm serpentine tensioner pulley bolt. You can try double-wrenching. Wear gloves and be careful. My wrenches kept coming loose. It started rounding the bolt and each time the belt came off of the power steering pulley.
You can use extra-long wrenches, but I couldn't find any in my area. The only way that worked for me was with the serpentine belt tool and a 15mm socket. I moved it all of the way up against the support on the top of the engine bay, carefully pulled it down, and I slid the belt over it easily. Then it was two 10mm fasteners and 3 cables, the negative battery terminal, and the struggle to remove the serpentine belt tool.
For some reason it went on far easier than it came off.
Apparently you are supposed the replace the tensioner each time that you replace the belt, alternator, air conditioning compressor\pulley, or the power steering pump\pulley.
The tensioner costs as much as the alternator!
Imagine if you were replacing the $20 belt and you find out that you need to replace the $135 tensioner!
Imagine a mechanic telling you all of this, with inflated prices!
Some notes:
It is easiest to slide the belt over the idler than the alternator belt pulley, so do the alternator, then the idler last.
Toyota slightly changed their setup during the 2004 model year, with the newer versions requiring a slightly longer belt. Some brands offer both versions, but this information is difficult to find, and parts store employees don't know the difference.
Toyota of Rockwall will ship this to me for $16.38, so I don't understand choosing aftermarket and possibly getting a belt that doesn't fit.
You are also risking stripping something while you try to make it fit.