Let's tip those scales.
Getting their Paycheck
Libra lives for balance and harmony, so that couple of days when they deposit a check and the account balances are #Winning, a Libra feels independent, rich and generous, thereby sexy. (Until they blow it all on #Fashion)
Getting New Clothes
Speaking of #Fashion, clothes and style are particularly important for Libra, so even if their little hearts shudder when they drop that 90 bucks on a new pair of shoes or a leather vintage member's only jacket, they'll have a fashion boner for a good long while every time they slip into the new digs. (Until next season, of course.)
Being in a Stunning Environment
If you really want a Libra to feel sexy, bring them somewhere where aesthetic is obviously the priority. Even being in a fancy hotel lobby (as long as they're dressed right, which obvi they will be) makes Libra feel they belong, and they have some control over the world. And then they will make out with you.
Figuring Something Out
Libras love contemplation and long, winding dialogues, so when they land on an excellent way to articulate a point without getting tired, or finally put together the reasoning for something, they have an intellectual orgasm (followed very possibly by real orgasms)
If your Libra can get you off, they'll get off. Libra is all about reciprocation, so when they see you enjoying their moves and sexual incantations, you can be they're loving it as much (if not more) than you. This is why being vocal is important, and making sure they see that you're having fun.