I've not used the LRP charger before but from a Google search it looks like you just plug in the usual red/black banana leads into the side.
I used to have the exact same 3s battery in my CoreRC transmitter and I luckily got the correct charging cable with my charger.
This cable set will fit your charger and also comes with the exact extension you need:
http://www.ebay.co.uk/itm/Core-RC-UD...4AAOSwGYVW9je6
you'll also need a 3s JST lead too.
Or if you want to cut straight to the chase, buy this:
http://www.ebay.co.uk/itm/8064-RC-4m...UAAOSwQYZWxHfD