You can do this with constructed lists. The key is to start by creating a predefined list with all the items that need to potentially show up in the final constructed list. So for your example, it would look like this:
1. apple
2. orange
3. grape
4. car
5. boat
6. airplane
7. other
Then we use constructed lists to split that list into the lists we need for each question. Continuing with your example, the constructed list instructions would look something like these:
Add(list1, 1, 3)
Add(list1, 4, 7)
After setting the select question to use those constructed lists, we create one final constructed list that has all the items chosen from each select question. If your questions are named "q1" and "q2," the instructions would be this:
AIC(q1)
AIC(q2)