if the arduino IDE will work an AVRISP MK2 the "sketch" can be written straight to the ATtiny rather than involving the arduino hardware. if your programming the arduino hardware to act as the ISP and the IDE can control the actual AVR ISP unit then why not just program the mcu's (any be it the mega's or the tiny's) directly with that, if i have one, if not yes program the arduino to work as the ISP saving people from having to buy one.