Audio input/output splitter for MacBooks without changeable input/output jack?
Yes, they are called 3.5mm 4 pin splitter, they separate a 4pin 3.5mm jack in 2 standard 3.5mm jack (1 for headphones, 1 for mic) as this one:

Startech.com 3.5mm 4 Pin to 2x 3 Pin 3.5mm Headset Splitter Adapter - M/F

you can read the comments, there are also some mac users that bought this splitter.