Here's an idea I used to do in the classroom when I was a preschool teacher.
Maybe it will work for you too!
Although I always had a regular sensory table in my classroom, with the older kids (3 and up) I liked to have sensory trays on a table as well. These were set up for individual play. I put two trays on the table across from each other, with a beach towel underneath to catch spills. Here's an example. The filler is dyed tiny alphabet pasta, and we put lots of little containers, spoons, etc in for the kids to explore. Love the touch of early literacy with the ABC pasta--the kids loved hunting for the letters in their names...
We usually colored the pasta as a small group activity but you could skip the kids' participation and just do it all yourself :) We gave each child a small zip lock bag and had them use a small scoop to put some of the pasta in the bag. Then we used liquid watercolor from Discount School Supply--the kids chose which color they wanted to use. The teacher squirts a little into the bag and seals it, and then the kids shake, shake, shake. Add more color if needed. Shake some more. Dump all the bags out onto a tray and shake it so it's spread out a bit. Let dry. I'm not really sure how long it takes to dry--we always did this before snack time and often wouldn't get back to it till around 1 or 2. By that time it was totally dry. I imagine it probably takes about half an hour to be usable. Easy peasy mac and cheesey :) This lasts for years, by the way.