Search the Keil knowledge base - there are several articles on this.

If memory's not a problem, you could just disable overlaying completely for those functions. Or not use automatic locals.

Or could you re-structure your code to not need the function pointers?
eg, use a 'switch' to select the required function from the "index", instead of indexing an array?

Note that calling functions by pointer restricts the parameter-passing capabilities, as parameters then have to be passed in registers.