I had a mate that sewed pockets on the inside to take armour on his normal jeans. but the problem is not the armour its the fact normal jeans will last about half a second when in contact with the road surface at 40mph and the armour will just fall out or move etc.
Much better off with some kevlar jeans, i have 2 pairs and they are as comfy as normal jeans although a little heavyer and hotter but not unbearably so. have also seen kevlar hoodies that a few stunters and streetfighter types like to wear. think it was made by grinfactor if memorie servs.
daughter likes her kevlar jeans because off the bike most ppl think they are just jeans but those that ride spot the extra stiching and tags so she still gets the biker factor and nod