How to resolve a “414: Request-URI Too Long” on SiteGround shared hosting of WordPress running Nginx? There is no direct access to Nginx configs

I am managing a WordPress site that is hosted on SiteGround and is being run behind Nginx which is returning “414: Request-URI Too Long” on some long post submits.

I have seen various solutions — like this one here on Stack Overflow as well as this one — that explain that config changes have to be made to core Nginx configs like this:

fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;

client_max_body_size 24M;
client_body_buffer_size 128k;

client_header_buffer_size 5120k;
large_client_header_buffers 16 5120k;

But shared hosting on SiteGround does not provide direct access to Nginx configs to make a change like that.

Is there any other way I can overcome “414: Request-URI Too Long” while running WordPress on Nginx but without mucking with core Nginx configs? Perhaps in the wp-config.php? If so, how?