SSRS distinct lookupset function URGENT

Hi all,

I have an urgent requirement for a report... Basically i'm using join(lookupset) to find unique group values which returns a sequence number.  This is my function 

Join(LookupSet(Fields!itemId.Value & Fields!UseByDate.Value & Fields!rackId.Value
    , Fields!itemId.Value & Fields!UseByDate.Value & Fields!rackId.Value
    , Fields!CustomerSeqNo.Value
    , "PickingList"), ",")

The problem is on some items there are multiple transactions, I want to remove the duplicates.  I found a blog http://blogs.msdn.com/b/bobmeyers/archive/2012/06/18/creating-short-lists-using-the-lookupset-function.aspx but could not get SSRS Report Builder to reference linq assembly.  My issue is 

Any ideas would be greatly appreciated as this is holding up a large project...