how to exclude

Hi

My outbound is changing the underscores to dashes and thats fine until i discovered that it breaks the js calling function. how can i modify the outboud rule so it does not apply to the following?

<a href="javascript:WebForm__DoPostBackWithOptions(new WebForm__PostBackOptions...

<preConditions><preCondition name="IsHtml"><add input="{RESPONSE_CONTENT_TYPE}" pattern="^text/html" /></preCondition></preConditions>

I tried    <add input="{RESPONSE_CONTENT_TYPE}" pattern="^text/javascript" negate="true" /> and <add input="{RESPONSE_CONTENT_TYPE}" pattern="^javascript:" negate="true" /> but no luck.               
Here are the rules...

inbound <rule name="1" stopProcessing="true"><match url="(.*)-(.*)" ignoreCase="false" /><action type="Rewrite" url="{R:1}_{R:2}" /><conditions><add input="{REQUEST_FILENAME}" pattern="^.+\.(axd|asmx|ashx|js|css|jpg|png|gif|pdf)$" negate="true" /></conditions></rule>

outbound 
  <rule name="1" preCondition="IsHtml"><match filterByTags="A" pattern="(.*)_(.*)" /><action type="Rewrite" value="{R:1}-{R:2}" /></rule>

Thanks