Note: The following solution is Solr 1.4 (and above) specific!
For more flexibility, I would recommend indexing your data with the NGramTokenizerFactory to do complete front and back wildcard searches. If you just want to search for substrings at the beginning or end of the string, consider using the EdgeNGramTokenizerFactory.
Here's a drop in replacement of the text field type which would accomodate your need:
<fieldType name="text" class="solr.TextField" >
<analyzer type="index">
<tokenizer class="solr.NGramTokenizerFactory" minGramSize="3" maxGramSize="15" />
<filter class="solr.LowerCaseFilterFactory"/>
</analyzer>
<analyzer type="query">
<tokenizer class="solr.WhitespaceTokenizerFactory" />
<filter class="solr.LowerCaseFilterFactory"/>
</analyzer>
</fieldType>
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