Congress has no more authority to participate in the deliberations of the EC than it does to participate in, or set the rules for an Article V state amendments convention.
No state EC delegation ever ran away because the simple fact is that the duties of electors are defined by state statute. Replace the term elector with delegate, and you have a situation identical to that of an Article V amendments convention.
Delegates will serve their states. They will have no attachment to any statutory authority under the US.
Article V now, while we can.