Trying to use insteadOf trick to use different SSH keys for separate github accounts - not working

Hello,

Here's what I'm trying to do, that i need your help with to make work:

I have 2 github accounts, each with their own SSH key: my home account (default SSH key) and my work account (alternative SSH key). I can create a virtual hostname in my ~/.ssh/config like so:

Host work.github.com
     Hostname github.com
     IdentityFile ~/.ssh/id_rsa-work

and then clone repos with:

git clone git@work.github.com/MyCompany/la-repo.git

However, I'm trying to use Go, which needs to access every repo host as 'github.com', and won't support my little SSH hostname trick by default.

I found out about the 'insteadOf' setting, and thought it would work. So I added this to my global git config:

[url "git@github.com:MyCompany/"] insteadOf = git@work.github.com:MyCompany/

and left the SSH hostname setting where it was. Then I tried doing:

git clone git:github.com/MyCompany/la-repo.git

But it won't work. With GIT_TRACE=2, I get:

$ GIT_TRACE=2 git clone git@github.com:MyCompany/la-repo.git
07:46:27.627557 git.c:344               trace: built-in: git 'clone'
'git@github.com:MyCompany/la-repo.git'
Cloning into 'la-repo'...
07:46:27.629623 run-command.c:626       trace: run_command: 'ssh'
'git@github.com' 'git-upload-pack '\''MyCompany/la-repo.git'\'''
ERROR: Repository not found.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights and the repository exists.

Can anyone help me with this?

Thanks

Regards,
     Asfand