you don't need to add summary results to the string running total as you can use Details results instead. this would involve having the srtMakerDateValues on the Details section and then altering it to bring in whatever field(s) you need to add to the string running total. this is just a sample to show you how to use this technique.
this is not an easy technique but it's pretty much the only way to get this kind of info in your cross-tab on the report level off of regular table objects. unless you wanted to do this on the database level with either a stored procedure or a Command object if your database has an aggregation function for text fields.
have a look at the attachment though as it is changed only slightly to bring in Details records...only the srtMakerValues formula is changed to roll up the individual Order ID's. you'll need to spend some time on this with your report to work it out as you need to decide what to roll up in the string running total.