Massive delete from a live production DB

Hi

Been reading some old threads (pre 9.x version) and it seems that the
consensus is to avoid doing massive deletes from a table as it'll
create so much unrecoverable space/gaps that vacuum full would be
needed. Etc.

Instead, we might as well do a dump/restore. Faster, cleaner.

This is all well and good, but what about a situation where the
database is in production and cannot be brought down for this
operation or even a cluster?

Any ideas on what I could do without losing all the live updates? I
need to get rid of about 11% of a 150 million rows of database, with
each row being nearly 1 to 5 KB in size...

Thanks! Version is 9.0.4.