In a word: No!
The issue with that MCU is that the PLL only multiples by 24 and must have an input frequency of 4MHz. (The reason is that this gives the 96/2 = 48MHz required for USB operation).
Once you have a 96MHz clock, the only post-scalar divider options are divide by 2, 3, 4 or 6. To get 40MHz from 96MHz would require a division of 2.4!
If you must have 40MHz then your only option is to use a 40MHz external oscillator, use EC mode and the 'divide by 1' option for the oscillator postscalar.
On the other hand, as @baileychic has pointed out, you can easily get 48MHz, or 32MHz using the PLL and dividing by 3.
As you are only wanting a faster Fosc for UART Baud rate purposes, then use the formula in the data sheet to find something that is close - but remember that a UART really need to be within 1-2% to be reliable.
Susan