I spray oil into or pour a little bit into a plastic bag , rub it through the bag , then stick the filter in and squeeze it around the filter. Ya don't get ya hands so messy that way and put a controlled amount on as mentioned above. I push the back of my half closed fingers into the inside of the filter whilst in the bag, ensuring you get good coverage up in behind the lip and back side also.
If I am riding that day or following day, I use canola cooking oil on the filter at times, this is probably not the recommend stuff though, for filters , but gets you out of trouble if ya run out.
I have also found , if you own a 2004-08 bike, you can get 2-3 rides at times before the filter needs a replacing. I find on the 2014 bike, every ride the filter just about needs doing , then the air box needs a clean also.
Cheers