I've just remembered something else I used to do with ds at that age and thought I would post in case it helps (although you may already be doing something similar anyway).
It's supposed to help encourage them to play more on their own and to develop their language skills, but I just liked it as an alternative activity.
Firstly, set aside a half hour of time where you won't be distracted. Turn off telly/radio/music so there's no sound distractions. Make sure there's lots of toys in reach.
Take your child's lead, watch them play and just comment on what they do - apparently it helps them focus on that toy for a bit longer. Only get involved if they ask you to, try to just observe. Absolutely NO questions allowed - it makes them stop what they're doing to process the question and whether they should answer or not.
E.g. "You've got the red ball. You're trying to fit it into the shape sorter. Uh oh, doesn't fit into the square shape."
You don't have to keep up a running commentary constantly, don't be afraid of silences.. just every minute or so (depending on how focussed your child is on the activity). Allow them to wander and choose something else, just comment on their focus of play.
I actually found it really really difficult (I know it sounds easy when writing it down!) - I kept slipping in questions at the end of sentences for a start, lol! "That doesn't fit, does it?" DOH! I did find that a) it filled up some time, b) meant ds was focussed for a bit longer on his play and c) encouraged him to play a bit more independently.
Hope this gives you something else in your arsenal of entertainment!!