A few ways that may work.

a) (I used this method, just to even out some lumps) If your cover is slotted, lift it and apply tape, working your way around. Like this guy (from about 25:00) https://www.youtube.com/watch?v=mRV6FC7RDvE

b) use some low profile adhesive cable clips, all aligned clockwise. When installing the cover, push in and rotate so the clips engageon the spokes, like a bayonet light bulb.

I can't see any smaller than about 5mm though, you'd probably want ~2mm for typical spokes
Or install them as shown here:

c) use some binding posts and pull the two sides of the cover together. as pictured here: http://www.dyma.com.au/DYMASLInstructions.pdf

I ride a Kestrel 4000 Pro which has very narrow seat stays, so I had to safety wire the cover to the NDS and DS spokes where they cross. I tried taping a bunch of different ways, but it would always pull away and rub - mostly because the cover would get wavy. I ended up taping it on and then poking two holes through the cover at each point the spokes crossed (NDS) and in the middle of each NDS spoke cross points to the DS spokes. I ran the wire so that the tie was inside, and then I covered the wire on the outside with a small tape dot. I had to adjust the wire tensions to get the cover wave-free and used tape to make the transition from the cover to the rim surface as well (Mavic Ksyrium). I ran it with no issues or adjustments for 2 seasons and only removed it when I eventually bought a disc.

Is it the Aerojacket, homemade, something else?

I have a homemade fiberglass cover, and just thought of a way to deal with this... Make each side in two different pieces. The first one goes from the rim to maybe half way to the hub. Tape this to the rim and also to each spoke. Then the second piece overlaps it slightly, and you tape this to the first piece. Should be solid and hug the spokes as well as possible.

Its the wheelbuilder aerojacket. I'd hate to cut a line into it if at all possible.

I had a similar issue (also old P2) and fixed it with self adhesive aerospace grade velcro which i cut in 2” by 1” strips. Stick the hooks on the cover under the spokes; then apply the loops over it with a spoke in between so it holds the cover tight against the spokes. You can still remove the cover whenever you like.

Ya, you wouldn't have an overlap anyway.

If you want to try DIY, this is what I got in .010" thick. It's more brittle than ABS, but it's lighter and very uniform: https://store.acpsales.com/...erglass-sheets-black