I use that concealer for under my eyes, and yes it is very dry and pasty, But that makes it perfect for covering up imperfections.
Right before I put on the concealer, I use a Vitamin E under eye moisturizer found at the Body Shop. It comes in a little pink tube, and I use the size of a pin head for each eye. The moisturizer is about 18$ i think, but it works really well with the MAC concealer. If you go to the Body Shop you can ask for a small sample of the moisturizer to take home with you to try, so you will know if it works for you before you buy it.
Best of Luck