You can solve this problem by organising your training camps.
Your goal is to have your one TC20 queued up with as many trainings as you can, a second training camp being levelled so that it gets to TC20 as soon as possible, a third training camp queued up with level 4 or level 11 trainings (whichever is slower - is it 4?) to mop up any excess recruits you have, and a fourth training camp idle.
To get there, you’ll have to clean up your surplus heroes by feeding them to someone, so you can then carefully shuffle your recruits and food between training camps. It’s not difficult, but it can be a bit fiddly.
When you are organised in this way, you will reduce the stream of heroes you are producing to a dribble. You’ll have one chance every two days of producing a 5* hero, albeit only a 5-7% chance. When your second training camp hits level 20, that will become one chance a day, you will start work on levelling your third camp, and your whole world will be wine and roses.