Yes you can. You can't land en route because, as in real life, taking off again needs a new flightplan.
Do the following.
Step1
Create a flightplan in the normal way landing at an airfield close to where you want to start from. I chose London Stansted to Andrewsfield. Don't forget to choose how you want to go - IFR low level, high level, VFR etc. I chose IFR low level (type 2 - see later)

Step 2
Create as many intermediate waypoint as you want by dragging the planned track to airports, VORs, NDBs, intersections etc
I chose all airports around the London Zone.

Step 3
Save the plan in the normal way but NOTE WHERE THE SYSTEM IS SAVING YOUR FILE!

Step 4
Open up the saved file with Notepad or Wordpad

Step 5
Paste in a copy of waypoint 1 (starting airport) as the final one. make sure you change the waypoint number so it's in sequence and you can either delete the original last waypoint (Andrewsfield in my case) or make the new last waypoint an additional one.

Make other obvious changes to the file text (destination!) and save with a NEW name.
Voila! you have a new circular flightplan. Enjoy it!