To slip one purlwise, insert your right needle into the next stitch from right to left (just like you do when you purl), just keep the yarn in back.
Next, wrap the right needle with your yarn going under, then over.
The yarn is now in back ready to k2tog.
When you do knit those 2 together, it may be a little awkward since the yarn is coming over the needle, but just insert your right needle into the next two stitches and knit them. It'll work out.