TrialPay is bringing the concept of enticing shoppers with the latest tabloid magazine, a pack of gum or a Snickers bar from the line at the grocery store to the online checkout world.

However, there’s a twist: If you bite, you’ll also get a discount on your original purchase.

Up until now, the Mountain View, Calif.-based company’s offers were most likely seen by people playing Facebook games.

Through a fairly exclusive partnership with Facebook Credits, TrialPay can offer a virtual good for free if a player considers buying another deal, like a cup of Starbucks coffee or a Chipotle Mexican Grill burrito.

TrialPay’s founder and CEO Alex Rampell explains that Starbucks or Chipotle pays TrialPay for the sales lead, and TrialPay pays FarmVille. Rampell said it’s a system consumers are comfortable with, because they are often buying physical goods, rather than intangible goods.

TrialPay’s new service, which is coming out of a long beta today, is bringing these alternate payment options to the online shopping cart. The goal is to convert more sales before they are abandoned at the point of sale.

One of its guinea pigs was MediaMall Technologies, which sells online streaming TV subscription packages. It offered customers a $15 discount on its PlayOn Premium software (normally $40) in return for signing up for a particular offer.

One such offer required users to also sign up for a GameFly subscription, which sends videogame rentals to your door, or a RealPlayer SuperPass.

Rampell said MediaMall immediately saw a 10 percent increase in revenue and a dramatic increase in average order value. The increase in average order value was due to the fact that it received a bonus commission based on every in-cart offer completion.

TrialPay is calling it a hosted shopping cart because it also handles the various payment systems, including PayPal and credit cart providers, on behalf of the retailer.

But game sales have been weak in 2009, even as movie theaters set box office records. What gives?

I’ll let someone else try to explain the movie side of the ledger (although those box office numbers aren’t always what they seem to be). But it turns out that there’s a simple explanation for game slump: It’s that gamers are huddled in their basements playing Grand Theft Auto over and over and over.

Gamers are indeed spending more time playing videogames, say new data from Nielsen. It’s just that gamers aren’t spending more money on games. Instead, they’re playing the games they have, buying used games, and increasingly turning to game subscription services.

Here’s the argument in chart form–you can get a summary here or download the full report here (PDF). Click on the charts to enlarge:

Hours played:

Used games purchased:

Subscription rate:

All of which explains why Best Buy (BBY) and Wal-Mart (WMT) are both getting into the used game business and why Blockbuster (BBI) and GameFly are expanding their game rental business. Now, if you’ll excuse me, I’ve got to get back to my game of Hover Kart.