Depending on how long and how often you need to do your testing, you can do a DL of the BES software, install it, and then contact RIM to get a temporary SRP that will allow you to do real testing of a BES as you would be implementing in production. This is a good way to do it because in my experience BES changes are fairly infrequent, and usually only occur before deploying major installs, upgrades, moves, SPs & HFs). Of course, you would need the rest of the lab infrastructure (Server HW, AD, Exchange, a test HH, and connectivity to the Internet), but other than that, it's an easy way around it. VM's, would also be a good way to approach this if you don't have the HW.
When it's time to do another big change, go through the same process again. You'll be able to recall stuff you've forgotten since you last did the install, refresh your skills, and be primed for when you do the prod upgrade.
RIM does give out separate SRPs, which you can also do for your lab (this way you can keep it up for good), but you'll need to pay for it in addition for all test licenses. If your company is willing to pay for it I'd go for it, as ideally it would be great to have a QA environment to test in!
"Different" question for you admins...
