A script to simplify WSL installation via lxrunoffline https://github.com/DDoSolitary/LxRunOffline/wiki

Install-WSL.ps1

param (
  [Parameter(Mandatory=$true, Position=0)]
  [ValidateScript({
    if(-Not (Test-Path $_)) {
      throw "File does not exist"
    }
    return $true
  })]
  [System.IO.FileInfo]
  $RootFsTar,

  [String]
  $Name
)

$ErrorActionPreference = "Stop"

$WSLRoot = $PSScriptRoot

$ExtractDir = "."
if ($RootFsTar.Name.StartsWith('alpine-')) {
  $DefaultName = 'Alpine'
} elseif ($RootFsTar.Name.StartsWith('fedora-')) {
  $DefaultName = 'Fedora'
}

if ($Name.Length -eq 0) {
  $Name = $DefaultName
}

lxrunoffline.exe i -n $Name -f $RootFsTar -d "$WSLRoot\$Name" -v 2 -r "$ExtractDir"

if (-Not (Test-Path -LiteralPath "$WSLRoot\$Name\ext4.vhdx")) {
  wsl --set-version $Name 2
  rm -Re -Fo "$WSLRoot\$Name\temp"
}

It will install WSL into the directory where this script is in.

Usage

.\Install-WSL.ps1 -Name Alpine .\alpine-minirootfs-3.12.0-x86_64.tar.gz