Only have three torrents active at a time so as not to divide my bandwidth too much, and
Typically seed for weeks at a time so as to give the ratio time to build at such low speeds. (I typically try to seed up to 10.0x, but you know, with old seeds, that’s not always possible to do even with weeks of seeding. :) )
Seeding in this way may not be very effective, but it makes it at least feasible.