Q:

Dynamically get n'th element of vector in Simulink

I have a vector [-1 1 -4 9 7] stored in a constants block.  I also have signal which contains a scalar which is determined from other parts of my Simulink code.  Let's call that scalar, 'n'.  How do I extract the n'th element of my vector? 
Example:

A:

The easy solution I can think of is making a custom block and just adding a Multiport Switch to it. 