Nope, the mic wouldn't work, I think. You can try but I don't think the contact surfaces match for a standard mic plug. One splitter is also a lot cheaper than two earphones.
Another option is obviously to buy a dedicated mic, either table mounted or snap on for your headphones. Then you'd be able to get a properly amplified condenser mic to get a much clearer sound than that tinny sound you get from a mobile quality mic. USB powered mics are probably the cheapest condenser mic option. They need more power than a 3.5 mm jack can produce.