I can't think of anything.
I figure by now this situation has already played out, but I'm gonna reply anyway in case someone later finds it in a search or for future reference.
I've been in this situation, once, and I know how desperate it makes you because it was the single time in my life I've actually used someone else's syringe.
Most of the time though I've been able to find at least some late night source of a new needle and syringe. Either from another junkie I knew, or from a 24/7 needle vending machine or 24/7 emergency department.
Apart from trying to track down a new one though, using via a different route than IV is the only option I can come up with.
I mean there might be other medical devices that use a standard luer fit that can connect to the syringe and be used to administer the drug, but nothing I can think of is anything people are likely to have at home.
Other than that I've got nothing that I don't think is only going to result in wasting even more heroin than just using another route, and probably with the bonus of bleeding everywhere on the attempt.
Sorry