Digging in to the dark magic of postgresql, i discovered that the integer to boolean cast can be changed from an exlicit to an automatic coersion. Then changed back when done...
update pg_cast set castcontext='a' where casttarget = 'boolean'::regtype;
Then load with pg_dump.
When done, set back the casting to its default with...
update pg_cast set castcontext='e' where casttarget = 'boolean'::regtype;
Important note: don't do this unless you know what it involves. The catalogs aren't guaranteed to be compatible version to version, and something that's safe(ish) to do now could be quite bad to do in a future version, or not work at all.