It can be done, but not well. The Allstar and similar systems are really intended to be used with higher end interfaces that not only bring audio between computer and radio but also bridge some logic signals for PTT and receiver activity as well.
Thanks. With Echolink I use the Rigbalster Pro with a full duplex sound board. With the process switch set to on I will tx on my vhf to echolink. It took me a while to get the setup right but it works pretty well. I had hoped to do the same with Allstar.