Jim, I just went & played around with your idea. Instead of the "tray" I put the felt & a large spool cap on the end & pushed it up about 3/4" & inserted into hole. So we have all parts that came with machine except felt which I'm sure everyone has around or can purchase at fabric store.
The main piece is the extra spool pin that came with your machine. It's
item 33 on page 3 of the instruction book. The other pieces are a small
red ring of felt, included with just about every other Janome machine
ever made, except this one, and what Janome calls a "tray", also
furnished with many Janome models, but not this one. It's about the size
of the large spool cap (item 31 on page 3), but has raised sides. Your
dealer may have it, or can order it as part number 829803004.
To assemble this rig, we placed the *OPTIONAL* spool tray over the round
hole on top of the machine. The felt is placed over the hole in the
tray. The spool is place on top of the felt and then the extra spool
holder (item 33) is placed, pin down, through the holes in the other
parts and into the round hole on top of the machine.