While I haven't tried it you could buy an eBook from Aeroplan shopping partner Indigo who offers 2 Aeroplan miles for every $1 spent.

I just took a quick look and there are some best sellers eBooks for $2.99 so that may be an option. You have to provide your Aeroplan number when it transfers you over to the Indigo site so your purchase should credit but how long I'm sorry I don't know however it may may a cheap option to earn a single mile.