You can freeze the Virus, but being a real synth, it does not support fast bounce..only real time bouncing.. if you are having issues getting it to freeze, then right click on freeze, disable fast bounce, i also enable audible bounce and single bounce per track but thats just me.. ymmv :)
I only freeze when i am completed with the project or i run out of polyphony and since there is no workaround that does not involve real time I just let it do its thing, and if its polyphony thats the issue the value of freezing an instance is that you can then go and insert another Virus :)