Hi!
One way to do this is by creating a parameter and connect it to a text input box.
Then create a calculated measure that checks the value of the parameter and then chose the corresponding kpi, ie:
if [parameter] = 'kpi1' then kpi1
else if [parameter] = 'kpi2' then kpi2
...
...
Then use this calculated measute in your cross-tab
One problem is that you can't change the format dynamically depending on the chosen kpi, they all get what you specify for the calculated measure.
Another is that the user must type the exact name of the kpi. One way to solve this is that the text box filters a list with your kpi's and the user selects kpi from this list, also you create another parameter used in the calculated measure.
Hope this can give you some inspiration 🙂
//Fredrik