Hoping this is not too late, here is one solution. Not an ideal one but still one that can help in easy situations

WARNING: This is not ideal in all situations. Use common sense 🙂

Using the report's code behind feature.

- Declare an array to store the whole of the second dataset

- Create function to initialize (redim) the array to the number of rows in your second dataset

- Create a function to store rows of your second dataset on a row by row basis

- Create a function to retrieve the desired row by passing in one or more parameters

This will mimic SSRS R2's lookup function. If you expect the number or rows retrived to be more than one, concatenate them with VbCrLf.

Let me know if you need actual code and i'll whip something up