XSLT Find preceeding text node in mixed content element

How can i find the text node that directly preceeds the "specialElem"-element ("Foo-" in this example)? While all other whitespaces inside the "main"-element shall be preserved, the whitespaces in front of the "specialElem"-element shall be removed.

<main>
   Foo Foo 
   <someElem>
   Foo Foo
   </someElem>
   Foo Foo 
   <otherElem>
       <subElem>
           Foo Foo 
       </subElem>
   </otherElem>
   Foo-        <!-- the whitespaces here shall be removed -->
   <specialElem>
       Bar!
   <specialElem/>
   Foo Foo
</main>

Desired output:

Foo Foo Foo Foo Foo Foo Foo Foo Foo-Bar! Foo Foo

Thnaks in advance!