Here's my hack for holding 4 writing tools to my Moleskine small notebook. It's an elastic band that slides over the cover. It's made from a piece of 3" elastic cord that goes top to bottom and a piece of 2" elastic cord that goes left to right. I got at the fabric store. I pinned the tools in place and sewed it on my home machine. Cost, about $5.

Update:
For those of you who feel I wasn't forthright in supplying instructions, here they are:
1. Open the cover and wrap the 3" elastic around it top to bottom.
2. Stretch it so it's tight before you mark it to cut.
3. Cut it and stitch the ends together on you sewing machine using black thread.
4. Since the ends of the fabric fray when it's cut, take a lighted match and singe the ends of the frayed thread to stop any more misreading. Be careful and don't burn yourself.
5. Slide the stitched loop over the cover for a snug fit. If not repeat the process till it's snug and won't slide off.
6. Now cut the 2" elastic to wrap around the cover from spine to inside cover. What I did was place one of the writing tools on the cover and wrapped the elastic around it snuggly and measured that. Multiplied it by 4 and I got my semi accurate measurement. You'll have to play with this for a while to get it right. I added about an inch so I wouldn't be short.
7. Stitch the end of the 2" to the inside of the 3" and pin the elastic over each tool as you work your way from left to right. Make sure they are snug enough to slide the tools in and out. I stitched each one before moving on to the next one.
8. After you finished with the tool holders, wrap the 2" around to the inside cover and trim off the excess at the edge of the 3". Now stitch and your done.
9. Slide your finished holder over the cover and make sure everything fits snug. That should do it.

Hope this helps.