Per this question, it takes about 6 hours from launch to reach that orbit, and it's hard to imagine that another space agency could detect and realize the threat and program an early interception trajectory in time to take it out even if they happened to have a launcher on the pad capable of doing so.
If the offender was simply injected into equatorial retrograde orbit at geosync altitude, it might not hit anything immediately, but it would now be harder to take it out safely without turning it into Kesslerish debris, effectively giving it the initial collision for free. Carefully ablating one side of it with a great big laser could push it out of position, perhaps.
If the offender was a guided, self-propelled spacecraft, I don't think there's a chance of stopping it. Ground-based guidance could put it on a close enough course that onboard radar could finish the job.
About the only way I see a chance is if the launch trajectory is actively controlled from the ground, with insufficient onboard location capability for the spacecraft to get into position on its own. Then, conceivably, once the retrograde transfer orbit was understood by other nations, a massive military strike against the launching agency's communications uplink could take out the threat, but no half-competent evil genius would neglect that consideration.