In this OGR thread a so-called "RF battery" was used to convert the DCS Remote Commander from line-of-sight infrared to RF. Here's the photo from the thread.
I had to think about it for a while but it's quite a clever gadget … albeit somewhat spendy.
So you pop out one of the AAA batteries in the DCS remote and replace it with an "RF battery". Now, when you press a remote button, the "RF battery" simultaneously sends an RF signal in addition to the infrared signal. You place the purple base unit somewhere in the vicinity of the DCS base unit. The purple base unit receives the RF signal and converts it back to infrared for the DCS base unit to receive. So it's kind of like an IR Repeater...except the link from remote to repeater is RF.
If you're a determined DIY'er, I can imagine cobbling together something like this using low-cost eBay electronic modules for, say, less than $10 out-of-pocket.