Yes - the minijack out on the AE has the same dual-function as the minijack out on a MacMini or Macbook - you can take an analog signal out, as you do when you use the earbuds-connector; or you can take an optical Toslink s/pdif signal from them.
Then you just port that to a DAC that accepts an optical Toslink s/pdif, and which has RCA LINE OUT for connection to the speakers. If the DAC has volume control then you get a good way of setting a master level for the speakers. As the DAC will not send anything to the speakers unless it receives a signal from your computer, the speakers will go into standby-mode as they should, when not being used.
If the DAC in addition has Headphone jacks OUT, then you can use that as well.
A good DAC will run you from a couple of hundred Euros to about 1.400. I linked to the Impact Twin from tc electronics on the Mac page. That is about USD 400, and is what I have connected to my BeoLab 5s.
If B&O had put a nice B&O skin around a proper DAC, their stores would the thronging with people looking to buy their cool speakers for use with their computers.
I've heard good things about this one: http://www.headfonia.com/matrix-mini-i-balanced-dac/
Emotiva has a nice unit, the one mentioned by Rookie is good.
I'm also using a Grace m902 (now there's an m903 model). It is connected to an Airport Express, as described above, and the RCA Line Out goes to my Beolab 5000 amplifier.
With respect, to the people answering "Yes" above, including Steve at Sounds Heavenly - "No," you're not getting the best your active BeoLabs can do if you are connecting them directly to the analog out on an AE or laptop. In addition there's risk of damaging your speakers when you connect and disconnect them, unless you always switch them off when doing so.
Steve could probably do a nice business selling a proper DAC with the Toslink minijack>Toslink and RCA>Powerlink cables required to connect to the speakers.