It is possible, but quite a bit more involved. You have to set up the pin PmnPFS register to enable sending the signal and then you have to set up the Interrupt Link Controller to handle it. See sections 19 on the port and section 13 for the interrupt controller in the hardware users manual.
On top of that, you also need to let the Arduino IRQ manager class know what you've done or it can end up replacing your interrupt in the ILC.
Since you're going to have to interact with the IRQ manager anyway, you might as well just use attachInterrupt. I figured a way to trick the IRQ manager into thinking that you've attached an RTC overflow interrupt so that it will give you a slot in the table and then hijacking that slot to put in whatever interrupt you want, but that's mostly useful for interrupts that aren't implemented in IRQManager. For something like this it would be redundant since attachInterrupt is already set up and implemented. Here's some more on that.
Is there a particular reason you are wanting to avoid that function?