How To Check If Value Is In Array Or Mv-param?

I'm working with a dataset something like this:

TypeID Sales($)
------ -------
1 123.45
1 47.98
2 9.21
3 87.23
3 99.88
4 123.43

And a multivalued parameter that lets the user select which TypeIDs specifically he wants to see:

ParamID ParamValue
1 Q1
2 Q2
3 Q3
4 Q4


And in my Report, I have data showing up something like this:

CountofAllSales: 6
SumOfAllSales: 491.18
CountofCustomSales: (count of sales with type specified in parameter)
SumOfCustomSales: (sum of sales with type specified in parameter)

The count and sum of custom sales should show -ONLY- the numbers from the TypeIDs selected in the multi-value parameter. But the CountAll and SumAll show everything, regardless. This is where I run into problems. I can't seem to find an "in" clause in the SSRS expressions. If the TypeID parameter was single value, I could write something like this

Expression for CountOfCustomSales:
=SUM(iif(Fields!TypeID.Value = Parameters!TypeID.Value, 1, 0))

However, since its multi-valued, that won't work. You'd have to write something like:
=SUM(iif(Fields!TypeID.Value = Parameters!TypeID.Value(0), 1, 0)) +
SUM(iif(Fields!TypeID.Value = Parameters!TypeID.Value(1), 1, 0)) +
....
SUM(iif(Fields!TypeID.Value = Parameters!TypeID.Value(length), 1, 0))

And obviously this doesn't work when you don't know exactly how many elements are going to be selected.

What would be ideal would be something like an "in" clause, but I can't find any such functionality or think how to write my own function:
=SUM(iif(Fields!TypeID.Value in
Parameters!TypeID.Values, 1, 0))

Short of modifying the StoredProc itself (and for me, that means red tape. :( :( ) can anyone think of a way to count/sum only the values specified in an MVP??