Sonnet, who makes a bunch of cool stuff, just released their SDHC Adapter for SxS Camera Slot. With it you can use itty-bitty SD cards in any Express Card 34 Slot. Like the one found on this camera.
Or even the one found on this camera.
You'll need a very fast SDHC card to be able to use this set-up on an ALEXA. SanDisk and Kingston both just released the fastest SDHC cards on the market. It's possible, but right now these new cards are still not fast enough to record your ProRes 4444 Log C masters. Besides, you'd probably just end up losing these little SD cards anyway...
But on the Sony F3 this could end up being half the price of a comparable SxS card. Then again, Sony's XDCAM EX codec is piss-poor when coupled w/ the F3's imager and ability to record in S-Log gamma. You'd be much better off skipping the SxS cards and XDCAM EX codec and going straight in with the ass-kicking 10-bit Apple codec ProRes 422 HQ via the new AJA Ki Pro Mini.
Or just give it 6 months. Or maybe 12 when Sony releases their newest flash memory cards.