I think your best bet is to find a smaller crochet hook to help you ease the yarn into the stitches. There really isn't a trick that will help you if your edge stitches are too tight. Another option is to work your domino knits are slightly larger needles so that the edges are a little looser.
Slipping the first stitch will only give you half the number of loops on each edge. This doesn't work well as it leaves gaps when you try to pickup stitches right along the edge. If this is the only way you can get a needle into the edge, you could pickup stitches as though you were knitting through the front and back loop of a stitch. It won't look as nice but it will allow you to pick up 2 stitches for every edge stitch.