"If a company doesn't want you as a consumer you might consider go to a competitor" doesn't sound like giving them power, quite the opposite.
git config core.sshCommand "ssh -i /home/your_user/.ssh/your_custom_key"
(I believe replacing "/home/your_user" with "~" works too) Host your_custom_alias
HostName git.domain.com
User git
IdentityFile ~/.ssh/your_custom_key
then instead of "git clone [email protected]:repo.git" you clone it with "git clone your_custom_alias:repo.git" (or you change the remote if is already cloned). In this case you don't need to have to change the git sshCommand option.