Why? just say you want to call a lawyer and have him present.
Any deal would have to be made with lawyer present, no objections, polite.
And call one anyway first point its possible.
Now, being an informant might be degrading but if you have genuine threats that you can help with, might as well cover all options.
Ok let’s go down this route. You say that and then they hand you a phone. Now what? You’re in an empty room, no internet access, no Yellow Pages nearby. What numbers do you press on the phone? I don’t even know a lawyer, let alone have one’s number memorized. That would really be a “they called your bluff” moment.
Call a friend / wife / parents - hey can you please find me a lawyer and call back - need him at address ...
Then they search and find someone and you shut up until one arrives. (most likely police/fbi will reschedule)
Helps if you actually have a social network, I have quite a few lawyer friends who would be present almost instantly or find someone willing fast.