Open the Window in mac where your images are stored.
Open your simulator another side.
Now drag your image from mac window to simulator,
simulator will open safari, and in a safari tab your image will be shown.
Tap & press down on image in simulator,
There will be message to "save image",
save image.
It will be added to your iPhone simulator.
Edit :
First just look at following image.

In iPhone simulator 4.0 ( iphone/iphone simulator ), itself it maintains a sqlite database for added images. So, if you want copy paste system - first make insert entries & then copy paste. That would be ridiculous way.
Ok. Let me explain simpler way of doing it.
- open the finder in which you have bulk images that you want to add in simulator.
- drag & drop first image into iphone simulator
- on image - tap & hold for 1 second.
- action sheet will appear - tap on save option
- repeat same process for all images
- this will do sqlite entries also.
- now, open the /Users/YourUserName/Library/Application Support/iPhone Simulator/4.0
- make a back up of Media directory. ( for example copy it & paste it on desktop )
- when you reset your iphone simulator, all images will be gone
- you need not to repeat all the process again, you have back up of it.
- just copy & paste from back up to 4.0
