To start the printer in service mode, hold the right, down and center buttons down simultaneously and press power. I've never really tried to figure out how long to hold them down, I just wait. You can tell you are in service mode by bringing up the menu ... you will see a much different set of menus. Once the printer is started in service mode, you can press the ink change button. The printer shouldn't initiate an auto nozzle check afterwards. (You may need to disable auto nozzle checking in the regular menus first, I'm not sure).
You can't send a nozzle check pattern while in service mode, but you can print normally, so you can send on from the computer. If there are clogs, the cleaning options in service mode allow some additional control, with CL-1 being a very minor clean using very little ink.