The conventional and formal way to handle equity includes a vesting cliff and a shotgun clause. The result would be essentially what you describe, but be sure to have it in writing. Hire your own lawyer if necessary.
OP, given the current plan, why not keep the copyright in your name until they let you join the company, at which point you can assign it to the company.
OP, given the current plan, why not keep the copyright in your name until they let you join the company, at which point you can assign it to the company.