I used a rubber eraser, cut it up into a suitable shape and jammed in in there. I've since sold the bike, but if I remember correctly, I had to tesselate a couple of pieces for it to hold in place and fully fill the hole at the bottom of the lever. It had the added benefit that if I accidentally pulled on the lever, it would spring back into place, unlikely electrical tape which could break or stretch.
I used a rubber eraser, cut it up into a suitable shape and jammed in in there. I've since sold the bike, but if I remember correctly, I had to tesselate a couple of pieces for it to hold in place and fully fill the hole at the bottom of the lever. It had the added benefit that if I accidentally pulled on the lever, it would spring back into place, unlikely electrical tape which could break or stretch.