You can add additional parameters to the Lookup page to include wildcards on the lookup. Edit Lookup.html and find the <#LOOKUP tag. Immediately after the popup=true parameter add the following-

StartsWithLabel="*=" ContainsLabel="*" EqualsLabel="=" EndsWithLabel="=*"

An example would look like-

<#LOOKUP POPUP=TRUE POPUPSTART=6 StartsWithLabel="*=" ContainsLabel="*" EqualsLabel="=" EndsWithLabel="=*" DEPTH=10 FIELD8=35 FIELD9=33 lclass="LookupDropdownClass" sclass="LookupDropdownClass" tclass="LookupTextFieldClass" orlookuplabel="<span class=text>Or Lookup</span>" keywordsearchlabel="<span class=text>Keyword Search</span>" buttonlabel="Lookup Now" addimage="images/add.gif">