You need a bit of js. You'll want to download the Splunk 6.x Dashboard Examples App
and check out the layout customization example, which you can see here once you install the app:
http://{yoursplunkservername}:8000/en-US/app/simple_xml_examples/custom_layout_panel_width?earliest=0&latest=
Whether this example works for you exactly... the answer is yes, js and if you wish css as well, but be sure to be careful with that because the .css that is used by default will a) override what you have or b) mess with every other dashboard in your app. So use with caution.
With Splunk... the answer is always "YES!". It just might require more regex than you're prepared for!
