This question is quite old, but I have the same problem on a new macbook pro.
I found Mathias Bynens' answer and installed Karabiner, but I would like not to remap optionn to control because I need the right option key to type all special characters in the left-hand side of the keyboard (which I use quite a lot).
My solution was to remap the left arrow key to control using the "Simple modifications" pane on Karabiner (left_arrow to right_control), and then mapped control + right_arrow to left_arrow using the complex modification below.
So now right control is where my fingers expect it to be, next to option and command, and to use right arrow I press and hold the actual right arrow key (i.e. right control) and then use the left arrow key.
Here is the complex modification (to use it, just copy it in a new file in the configuration directory of Karabiner under assets/complex_modifications).
{
"title": "Ctrl + right arrow to left arrow",
"rules": [
{
"description": "Ctrl + right arrow to left arrow",
"manipulators": [
{
"from": {
"key_code": "right_arrow",
"modifiers": {
"mandatory": [
"right_control"
],
"optional": [
"caps_lock",
"option",
"command",
"shift",
"fn"
]
}
},
"to": [
{
"key_code": "left_arrow"
}
],
"type": "basic"
}
]
}
]
}