Alternator Renault Espace II

Hello, I'm new to the site and I'd like to introduce myself.

I'm from Cádiz and I have a Renault Espace that I've been modifying myself, and so far it's running great, except for one small problem. I don't know how to tighten the alternator's locking nut. It's in a place that's almost inaccessible to my hands and tools, but I need to hold the nut while tightening the bolt from the front of the engine. How can I do this without having to remove the engine or the injection pump?

Thanks in advance.