Lo and behold! ...suddenly I remember that I had a roll of duct tape in my pannier!
What we did was to tape the back of the tire with 2 layers of 3" & 4" duct tape over the cut area. Although it is unnecessary but for double (triple?) protection, we cut (using a SWISS KNIFE, ahem!) the old tube into 2 pieces of 4" & 5" and slice it into half so that it wrapped around the new tube right below the cut area. Then, slot everything into the tire.
Actually, this was my original idea before I remember about the duct tape. I was playing safe because we still have another 60km++ of riding untill our destination.
After everything is set properly into the rim, we cut another 4" of duct tape and cover the cut area from the front to prevent small stones or pieces of glasses to slip into the cut area and damage the inner layer of duct tape.
Surprisingly everything went well! After 30km, I replaced the outer layer of duct tape and we keep riding for more than 60km and the tape is till there! YEEAAH..!!!
Duct Tape....definitely a MIRACLE TAPE!