I assume the OP wants something with the accuracy of a Wacom stylus, not a mushy capacitive rubber blob.
You could get a cheap Galaxy Note stylus and tether it to the Surface with a string maybe. You may be able to cut it in half and have it still work, then you could attach that to a finger somehow. And since it has the button, you get to keep that function. The stylus from my Note 4 works well on my Surface Pro. I prefer the larger and easier to hold Surface stylus, but it works.