I think you just have to let them ripen on their own. This information may help somewhat if you want to check it out: http://www.funadvice.com/q/avocadosripesingleavocadoboughthardcutopenpick
Place them in a paper bag with a ripe apple or banana and leave out of the fridge- in 1 day they will be ripe.
Placing it in a container of uncooked rice, placing it in a bag of flour, brown bag, or with bananas.
My mom does this a lot with almost any fruit :}
Really? Hmm, I didn't know that, interesting.
Wow, that's awesome.