From my experience, you will need to use a Groovy Script step.
For example, if you have a step before your request that is a script, you can use something like:
context.setProperty("ProviderId", "SHL")
Then in your request, use:
<ns:ProviderId>${ProviderId}</ns:ProviderId>
Of course, this doesn't buy you much by itself. There are few ways to vary what the context.setProperty("ProviderId", "SHL") line will set. You can create a collection and iterate over it using something like:
def providers = ['ABC', 'DEF', 'GHI', 'JKL']
providers.each() {
context.setProperty("ProviderId", it)
testRunner.runTestStepByName( "nameofteststep" )
}
Where "nameofteststep" is the name of the Soap Request test step. This might sound odd, but if you right click the test step and disable it, the groovy script will still be able to execute it but it will not run sequentially. By that I mean that the groovy script will run it 4 times, but it won't run a fifth time when the script is complete because it is after the script. Then you just need to keep in mind that each load test thread makes four requests, but I am pretty sure that the SoapUI statistics will take this into account for you... might want to keep an eye out for it, though.
Alternatively, you could check the 'threadIndex' and set a the context variable based on that. A bit like this here: Log ThreadCount.
You could also use a collection without a loop and increment an index that you save as a testcase property and send the string corresponding to the index.
Personally, I think the first way is the most straightforward but I can provide an example of the other ones if you like.