Phone up your supplier, speak to 'em nicely and they might let you stick it on your laptop and desktop. Doubt it with Siemens but I know that Omron let me put a copy of their software on my desktop. I have it on my laptop for service jobs etc but I needed it on my desktop for printing out the software to give the documentation to customers (obviously my desktop never goes on site so the software on the laptop and desktop are never used together).
Worth a shot.
I phoned Omron, explained the situation to tech support and they said that as long as I wasn't using the two copies together then they didn't see a problem with it.
I'm with the other lads when it comes to robbing software, I think that the existing protection is problematic enough to us 'honest' engineers in that it can sometimes make your job harder (although Siemens do provide a "get you out the brown stuff 14 day license).
I'd hate to see hardware dongles coming in.