This is a pain because I cannot update the JDK to a version I'd like/have to use.
Well there is an option.
Download the desired JDK from the regular location.
Open the executable file using 7-zip or something similar. The executable contains only a single file named tools.zip. Unzip that file to a location where you want the JDK installed and you have write access to, for instance
This will create the installation structure, although many of the jar file components are still compressed. These must be de compressed using a tool provided with the JDK itself, unpack200, that is found in jre\bin.
Locate all .pack files using
dir *.pack /s/band de-compress each of them using upack200:
c:\development\jdk-8.20\jre\bin\unpack200.exe -v -r path\file.pack path\file.jar.
The '-v' option provides for verbose output and the '-r' option removes the original pack file afterwards.