[mott]

I haven't seen the actual bumper construction but using Figure 4-4 (Bumper Cross Section) and the "1 in. limit for hard parts", you can add right at 14.5LBS to a otherwise "normal" set of bumpers simply be using 1"x1"x.125" steel angle iron (.8lbs per linear ft) on both the top and bottom of a full-perimeter set of bumpers.

While this might be considered playing in the grey area of the Question 480 response, it wouldn't seem to be in violation of R24 in any way I can see.

Further, by using .1875" or .25" angle iron you could increase your bumper weight even more!