Modifying Interrupt Vector Table of Atmega32
The answer is in avr/interrupt.h line 228 which decides to use jmp on ATMEGA and rjmp on other micros. Presumably you could override it back to rjmp as long as you make sure your ISR's address is within the allowable range for rjmp.

The documentation for avr/interrupt.h as mentioned in another answer explains how to mark the ISR as naked to avoid any function setup/teardown overhead. You could even write the function using inline assembly, but you can probably get exactly the instructions you want from C, too.