Hmm. I guess you could make one but I doubt you could in 15 minutes. Getting the spacing right and stuff would take a longer. I know it is possible but to be honest I think it would be more work than you think. If you have a band saw, drill and taps and some steel laying around I guess it is possible.
Edit- I thought you were talking about making the tool I listed above. Yes you could make that bar design but I have used one and getting at the rear springs is a *****. I know it just takes time and can be done but with this tool you can do two springs at a time/one cylinder at a time.