Are you willing to file a lawsuit if you have to?
If so, there may be meaningful options. If not, you can still exercise those options, but you'd just still be bluffing.
- As in most professions, most lawyers have bosses. If this guy works for a firm and does not have his name on the door, he's probably got someone he answers to. You could call a partner in his group and explain that you're trying to resolve this without litigation. If my boss found out I was blowing someone off -- and they seemed like a credible litigation risk -- I would be in a bad position.
- A lawyer's real boss is his client. Call your former employer and let them know that because the lawyer won't write you back, you're preparing to move forward with litigation.
- Draft a demand letter. This stops short of litigation but suggests a level of seriousness that a routine phone call or e-mail does not, and the lawyer should definitely take that to his client to decide how to respond. There are lots of free resources explaining how to do this. I haven't read it, but I'd guess that this FindLaw explainer is generally reliable.
- Try to engage the services of a mediator, maybe through a local chamber of commerce or BBB.
- Launch prelitigation discovery. I suspect that the availability of this option will depend on your jurisdiction, but in some states, you can start demanding information to use in litigation without actually filing a lawsuit.
In the end, you are right that you can't be forced to hire an attorney, but you also can't force an attorney to negotiate with you if you aren't involved in litigation. If you do get sucked into litigation, though, you can play this to your advantage by creating an extensive paper trail. Judges do not like to see that they've been drawn into a case that could have been negotiated away.
As a side note, I'm not surprised he's talking with you if your responses suggest that you may still hire a lawyer. In most circumstances, I would probably wait for an opposing litigant to unequivocally say that is representing himself before I dealt with him.
Dealing with an unrepresented party is inviting trouble, as many pro se litigants -- especially the ones who lose -- are itching for a reason to file an ethics complaint against some "crooked" lawyer. If I think someone is going to hire an attorney, I'm going to give them all the time they need to do that and avoid even the appearance that I'm trying to exploit them while they're unrepresented.