Jason,
Sorry for your loss...
I used to have a sailplane when I was a kid, that had a time fuse at the horizontal stabilizer. The stabilizer was held down with a spring. You would lid the fuse, and throw the plane. After the fuse was all "burned up", it would release the HS and the plane would land. It worked like a charm! Maybe you can try something similar?
Take the ashes and tie them into a cloth. The cloth is held together with the fuse. Attach the cloth upside down to the P4. Set the fuse and take off. Once the fuse is all burned up, the cloth will open and the ashes fill fall out. Pretty simple. Take a look at the link...
How to Make Slow Burning Fuses from Yarn, Sugar, & Potassium Nitrate « Mad Science
Thanks,
Kmd
p.s. The fuses that I have seen lately smoke a lot. Mine did not do that. It was not really burning but rather "simmer". (Sorry, English is not my native language and I cannot come up with a better word...)
p.p.s. Maybe it is better if you have the fuse open a small, very light box with a spring loaded lid...