Frequent Flyer Bonuses points out an interesting promotion to earn 5000 bonus GarudaMiles plus 3 miles per dollar via Rentalcars.com. The offer is valid through March 31.

GarudaMiles is the frequent flyer program of Skyteam member Garuda Indonesia. They’re also a transfer partner of Citi ThankYou Rewards.

Here’s the interesting thing. The 5000 mile bonus doesn’t say it applies to first rental only, it seems like it would apply to each rental via RentalCars.com made using their referral link that you complete during the promotion period with no minimum car size or rental length.

Three RentalCars.com one-day rentals, which can be accomplished for less than $100, would earn enough miles for a short-haul Skyteam redemption.

Here’s the award chart that applies to most partner award bookings like Etihad, ANA, and Skyteam members like Delta.

You can book a Delta award that’s under 1000 miles in distance for 15,000 GarudaMiles. Here are some sample flights less than 1000 miles in distance:

Under the offer terms it appears you can leverage these rentals as many times as you want, and of course you can top off your GarudaMiles account with points from Citi ThankYou Rewards (if you have a Premier or Prestige account). So redeem your points for Garuda Indonesia first class on their Boeing 777, for instance between Amsterdam and Jakarta (or London Gatwick and Amsterdam, here’s a review of that short segment).

Here’s the offer terms and conditions:

Book and confirm a car rental at http://www.rentalcars.com/?affiliateCode=garudamiles and complete your booking process

Earn 3 GarudaMiles for every 1 USD of spending on a car price, only through the designated site above
You must be an existing GarudaMiles member to earn mileages.

To be eligible to earn mileage, your GarudaMiles membership number must be inserted in the Driver Details page when making a booking on this designated website.

GarudaMiles are only earned when you have paid for, picked up and completed the car rental.
Please allow approximately 6 to 8 weeks after the drop-off date of your car rental for GarudaMiles to be credited into your

GarudaMiles account.

GarudaMiles will not be earned on the other items purchasable online such as Full Protection.

GarudaMiles will also not be earned on any items that you purchase offline when you are picking up the car from the local car rental company such as baby seat, GPS, travel insurance and one way fees.

GarudaMiles terms and conditions apply.

GarudaMiles will not be earned on rentals being paid directly to local supplier on arrival.

This could be somewhat valuable, buying miles at under 2 cents apiece and since the award chart is distance-based there are a handful of sweet spots. Although the award chart itself isn’t cheap by any means.

Still, I’m not going to take advantage of this offer for two reasons:

1. I’d hate to try to chase down miles from Garuda Indonesia that are supposed to be posted through a RentalCars.com affiliate relationship. If miles don’t post automatically I foresee pretty high transaction costs to actually get the miles promised.

2. Most redemptions require in-person ticketing at a Garuda Indonesia sales office. There are (4) in the United States in Los Angeles, Chicago, New York and Houston. Perhaps they’d work with you by phone or fax (there are forms involved), I haven’t done it myself.

File this one under really interesting, probably more trouble than it’s worth, but the kind of challenge that someone will take up and scale to good use.