Why create a custom question type, when you can use the ones that exist?
If I understood you right, you just need a simple 6 point choice? Have a look at the "array" question type. You can create custom scales. 3 point, 4 point, 6 point, 7 point, 8 point, whatever fits on the screen. OK, it looks slightly different to the 5 point choice, but it should do the job, shouldn't it? Or you take a list radio with 6 items. OK, then the items are lined up vertically, but you could set the column attribute to 6, then they should aline horizontally as well. Just have a look at the link below and browse through the question types. I am quite sure you don't need to create a custom question type. I might be wrong though, but from your describtion...
docs.limesurvey.org/Question+types&struc...tions+for+LimeSurvey