Hi Daniel,
Yes, although the pro version does have the environment feature, this is very doable in the open source version, there are several effective ways to accomplish this.
One way is to use a Properties TestStep. These can be used to load properties from a simple text file as part of a TestCase e.g. a file containing:
environmentName=QA Environment
invoiceEndpoint=http://localhost:9001
userName=test
password=password
These properties can then be referenced eslewhere in the TestCase e.g. to set Request TestStep properties/value using property expansions e.g. like
def environmentName = context.expand('${LoadProperties#environmentName}')
Note you can also supply the file name as a property that could be supplied as a project level property e.g. reference with ${#Project#propertiesFileName}
Also as a runtime parameter (-PpropertiesFileName=...) if running SoapUI from a runner script e.g. testrunner.sh. Note you could supply all your properties this way, there is also a -e enpoint parameter for the runner script.
See also http://www.soapui.org/scripting---properties/working-with-properties.html
Hope this gives you some ideas,
Cheers,
Rupert
Author of SoapUI Cookbook
