Try...
skin/reboot/modules/Product_Options/customer_options.tpl
Replace...
Code:
<select id="po{$v.classid}" name="{$poname}"{if $disable} disabled="disabled"{/if}{if $nojs ne 'Y'} onchange="javascript: check_options();"{/if}>
With...
Code:
<select style="width:100%" id="po{$v.classid}" name="{$poname}"{if $disable} disabled="disabled"{/if}{if $nojs ne 'Y'} onchange="javascript: check_options();"{/if}>
... That should make the select dropdowns stretch 100% of the container.
Unfortunately, you cannot 'wrap' text in the select dropdown options.