I know that you can make a USB mini B connection appear as an USB mini A, because I have seen someone do that. He just made a small ball of aluminium foil and shoved it into the connector. The pins that need to be shorted are next to eachother and at the side (but I don't remember if it was the left or right side), so it was still doable to get it in the right place. Micro USB is internally very similar, so it should be possible there too, but the inside is quite a bit smaller so it'll be a lot harder.
In your case it might be easier to solder 2 cables together. It is a bit annoying to solder USB cables together because the cables are shielded, but there are only 4 internal wires and the data rates are low enough that it doesn't really matter if the shielding is imperfect. USB OTG cables should have an A type connector, and they are generally relatively cheap and easy to obtain. To get the USB-C connector, use a cable that has a USB 2 type of connector on the other side (regular, mini or micro), to make sure that the cable only has the USB 2 wires (USB 3 cables have extra wires in them, which aren't really feasible to extend).