While making my second sampler afghan, I found that I needed to join the squares with slip stitch, but my squares had many carried strands and loose ends from color changes. I didn't want to weave in all the ends, but couldn't find anything on the internet about how to hide these less than desirable bits. The nature of slip stitch makes it less bulky than a single crochet join, but it also means the ends aren't hidden under the stitches. My method hides the ends and carried strands securely and even adds a zig-zag pattern to the slip stitch that adds some character when joins are made using contrasting yarn.
Begin joining yarn as usual, holding the two pieces with the right sides facing each other (wrong sides exposed). Slip stitch through both pieces in the far right corner (or wherever you want to start joining), and continue slip stitching across until you get to the loose end. Hold the loose end over the top edge as you normally would, going under the loose end for the first slip stitch. For the next stitch, move the loose end slightly down and slip stitch above it (essentially, the loose bit won't be in the stitch at all). Repeat alternating slip stitches under and "bypassing" the end, until you're satisfied with the join or reach the end. Because of the alternating stitches, you end up with a zig zag pattern.
If you have multiple loose ends, you can tie them in a square knot, ensuring the yarn stays flat against the edge, not too tight or hanging off loose. That will both ensure a clean and easier join, and that the loose ends won't unravel.
Once I'm able to take some pictures (or a video), I'll edit this post. Stay tuned!