Resizing Jasny's Bootstrap Fileupload form

Question

I'm not able to resize Jasny's Fileupload form. First I made a centered span8 with offset2. Then I put a simple input form into the span and set it to 'input-block-level'. That's working fine: the input form has now a size of span8.

I want to do the same with the Jasny's Fileupload. I tried a lot, but it didn't work for me. What I need, is a function that replaces the span3 entry in class="uneditable-input span3" with some kind of auto-resizing function, that stretches the input box to span8. Replacing span3 with input-block-level also doesn't work.

Another possibility would be a fixed value for the control button (maybe span3) and a for the input field (span5).

Any ideas?

<div class="row-fluid">
    <div class="container pagination-centered">
    <div class="span8 offset2" style="background-color:#FFCC33">


    <form class="form" action="someaction" method="post" enctype="multipart/form-data" style="background-color:#FFFFFF">
    <div class="control-group">
        <div class="controls">
            <input type="text" id="someid" name="somename" class="input-block-level" placeholder="well stretched box">
        </div>
    </div>

    <div class="control-group">
        <div class="controls">
            <div class="fileupload fileupload-new" data-provides="fileupload">
                <div class="input-append">
                    <div class="uneditable-input span3">
                        <i class="icon-file fileupload-exists"></i>
                        <span class="fileupload-preview"></span>
                     </div>
                    <span class="btn btn-file">
                        <span class="fileupload-new">Select file</span>
                        <span class="fileupload-exists">Change</span>
                        <input type="file" />
                    </span>
                    <a href="#" class="btn fileupload-exists" data-dismiss="fileupload">Remove</a>
                </div>
            </div>
        </div>
    </div>
    </form>
    </div>
    </div>
</div>