Last night, I created my own solitaire version of the game that I played while Annelies was working on schoolwork. It's based on some variants I saw on BoardGameGeek for the main game.
Start with the standard set. Go ahead and pull out your color of meeples and put one on the scoring card. Also, play the standard starting tile. Now, draw 32 tiles from the normal tile pool. These will be your supply. If you want a shorter game, you can draw less, but I found this number to last around twenty minutes of play. You should also shuffle and put aside the bonus tiles.
At this time, you start a normal game, pulling one tile at a time. However, if you have any valid move after placing the tile, you must take it. This means that sometimes, you won't complete something immediately because it would mean that you'd have to put a meeple down in an unproductive meadow or sacrifice one of your huts, but it adds some challenge to the game.
Play as normal, including the playing of bonus tiles, until you've gone through all of your initial stack. At this point, do the final scoring of the game. I did three rounds of this last night and ended up with scores around 110, 125, and 145.
I could think of some other variations. You could use two colors and setup some kind of scoring where you get double points for completing items which have both colors in use.