The quick way is to edit the plugin ‘function.js’ line 82, insert a comma after
'streetViewControl' : bgmpData.options.streetviewControl
and insert from line 83
'styles' : <copy and paste content of JSON here>
Other option is to add a new bgmpOption such as ‘style’ with a textarea on the settings tab and use the content in the function.js.
Both solution wil be lost on plugin upgrade…