I'm not so sure that bonded aluminum was a bad idea, and Trek at least did a very good job of it. But welded aluminum became very cheap to produce in mass quantities.
That said, while bonded aluminum is theoretically framebuilder-repairable to a greater degree than welded aluminum, I agree with HillRider that it's a dodgy operation and definitely ain't worth it in your case. The Reynolds 531 tubing is probably standard size, though, so a lug in the proper diameters and angle should be available if you really want to go for it. Also would be possible to do a local repaint if you want to do this on the cheap(er).