it simply needs to gain experience to get EV's
Correction: it doesn't actually need to gain experience, it just needs to be in a situation where it would gain experience. Usually this is the same thing, but in Generation V they changed it so you can EV train at level 100 (after you stop gaining experience).
You could possibly utilize your Unburden ability to maximize the effectiveness of Thief. Simply go into battle with Liepard without an item, use Thief, and voila!
Unburden only works when you actually consume the item, so going in without one doesn't work. This weird activating behavior is why Unburden is such a bad ability - it doesn't work when you switch out.
Honestly, I wouldn't bother with Leftovers or any defensive item on Liepard since it doesn't have enough bulk to survive a swift breeze let alone an incoming attack.
I would try something like:
EVs: 4 HP, 252 Attack, 252 Speed
Item: Normal Gem
Moves:
~ Fake Out
~ Taunt
~ Thunder Wave
~ Torment/Rain Dance/Sunny Day/Whatever attack you want
Your Nature might be pretty bad for this set, but the idea is that you can come in, Fake Out for some damage and to activate Unburden, and then disable the opponent as best you can before dying a quick death. Torment is useful against Choice users and defensive Pokemon that only run one actual attack (since you can Taunt to prevent a status move, then Torment to force them to Struggle next turn if they stay in).
It stretches what could be called "playable", but we are talking about Liepard here, so you can only do so much.