The roller-shop "Nomades" (place de la Bastille) does blade rentals.
http://www.nomadeshop.com/(click on the "location" -meaning "rental"- red tab on the left for details and fees)
I'm sure some other shops probably do that too, I'm only familiar with this one.
At Nomades, the fee is 8€ /day (5€ for 1/2 day, starting 2pm on weekdays). Add 1€ for the protective gear. I'm sure if you talk to them you can arrange to return the blades on saturday morning. Or keep them for the full week-end (16€) and enjoy the sunday ride as well!
Beware, they require a deposit with a 150€ check or an ID card/passport (last I heard, they wouldn't take a deposit off a credit card). And payment in cash as well, no credit card.