how to force drupal to create tables with ENGINE=MyISAM
The schema definitions can take an argument of 'mysql_engine', which defaults to 'InnoDB', in createTableSql().

In theory you could thus alter all the defined schemas with a custom module, and change the engine.

It's highly questionable to do so though. If you value your site and data, you should NOT use MyISAM unless you understand the difference the two engines.

Switch to a provider that supports InnoDB instead. MySQL itself defaults to InnoDB as of 5.5. I would be very suspicious of any provider that didn't support InnoDB.