I said I'd post this, and after a request - here it is!
This mushroom was made to accomodate a single Led on a string light set (I believe I made the hole 5mm wide), though it made need drilling (or rescaling) depending on your lights.
The 'head' has a small void to allow for the light to spread, and the base is spiked so that it can be stood into the ground easily.
BEWARE! - if you push your light too far into the head, it may become stuck due to the void.
Hope you have fun with these, let me know if you print them!