I'm not sure what the cheapest solution would be, but you could get a remote with RF to IR extender.

Basically the remote talks to the extender over radio frequency which then sends signals to the infrared receiver on the 990.

Harmony (and Monster) and Universal as well as others make remotes that do this. Not sure what the cheapest will cost though. If memory serves, typically the RF remotes tend to start at around $300, but you can probably find them cheaper. At that price point you also typically have to buy the RF extender separate.

I have the Monster AVL 300 and 1 Monster Optilink and it works well...but that remote is $600 retail. Similar in design and function to the upper end Harmony (actually OEMed for Monster by Harmony/Logitech).