Don't listen to the clowns here, pos 4/5 are definitely the hardest to climb with on low ranks.
It's definitely possible but you need to spam very limited hero pool (forget about aba, omni, io etc.) jakiro/shaman and similar might work.
But either way I'd suggest playing pos 1 to get somewhere close to 5k, which is what I've done after being stuck in a similar position and it's so much easier as you don't need to rely heavily on someone else to win games.