Installing single-ended LED in a pre-existing T-8 fixture with only one connection per side
Those sockets at the end of the fixture that the tube snaps into are called lampholders.

You are correct that fluorescent tubes have 2 pins on each end (a preheat filament is between them) and some ballasts do not use that feature.  To avoid having to make a bunch of jumper wires, manufacturers use a shorting lampholder which internally shorts both pins.  You are cursed with those.  

Virtually all lampholders come down to 3-4 different compatible styles (overwhelmingly one**), all of which I've been able to find online.  I've never had to abandon a fixture due to odd lampholders.  That seems even less likely with a shorting lampholder.    Get some non-shorting lampholders.  Done.  

In the future you avoid this problem either by making sure you are buying direct-wire LED "tubes" that feed from opposite ends (that's safer anyway) or buy those particular plug-n-play LEDs made for your ballast type (but then you have to maintain the ballast, no thanks.)

** I just overhauled a prewar fixture.  The 4' fixture was bulletproof drawn 18 gauge steel and weighed 10 pounds without the ballast. The lampholders were trapped in a weird way, but guess what, they were the most common type.   I put a T8 ballast in it, I go for the 90CRI real tubes, better light quality.