Prefix numbers with loadtesting

Hi,

I'm using soapUI 3.5, free version.

I want to make a loadtest. I need to make several variables unique for me requests to succeed.

I found a nice solution for this problem on the internet, now i'm using the following input in my xml to make the numbers unique:
00${=context.getProperty("ThreadIndex")}${=context.getProperty("RunCount")}.

While running the test performancetest i ran in to a problem.
The output of "00${=context.getProperty("ThreadIndex")}${=context.getProperty("RunCount")}" must be exactly 4 characters, otherwise my test xml won't be valid.
So if im running a loadtest with 5 Threads and the runcount will exceed 9, this number will get more than 4 characters and my tests will fail.

Does anybody has a solution for this problem?