Use a comparison operator for your WordPress `meta_query` key - inspired by http://wordpress.stackexchange.com/questions/193791/use-regexp-in-wp-query-meta-query-key

functions.php

add_action('pre_get_posts', 'meta_query_key_compare');

function meta_query_key_compare($query) {
		$meta_query = $query->get('meta_query');
		if(empty($meta_query)) {
			return;
		}

		$marker = '__tmp_marker__';
		$rx = [];

		foreach($meta_query as $key => $meta_query_part) {
			if(isset($meta_query_part['key_compare']) && in_array( strtoupper($meta_query_part['key_compare']), ['REGEXP', 'RLIKE', 'LIKE']) && isset($meta_query_part['key'])) {
				$meta_query_part['key'] .= $marker . $key; //so we can find it later
				$query->query_vars['meta_query'][$key]['key'] = $meta_query_part['key'];
				$rx[$key] = $meta_query_part;
			}
		}
		if(empty($rx)) {
			return;
		}

		add_filter('get_meta_sql', function($sql) use ($rx, $marker) {
			static $nr = 0;
			if(0 != $nr++) {
				return $sql;
			}
			foreach($rx as $key => $meta_query_part) { //replace the markers
				$sql['where'] = str_replace(
					sprintf(
						".meta_key = '%s' ",
						$meta_query_part['key']
					),
					sprintf(
						".meta_key %s '%s' ",
						$meta_query_part['key_compare'],
						str_replace(
							$marker.$key,
							'',
							$meta_query_part['key']
						)
					), $sql['where']
				);
			}
			return $sql;
		});
	}