Belboon integration, custom GET params

We are currently trying to integrate belboon into our shop and have the following code in our template:

[{ if $oxcmp_shop->oxshops__oxadbutlerid->value }]
    <!--Adbutler-->
    <p>belboon</p>
    [{assign var="discountnetprice" value=$basket->getDiscountedNettoPrice()}]
    [{assign var="currencycovindex" value=$oView->getCurrencyCovIndex()}]
    <img src="https://www1.belboon.de/adtracking/sale/[{$oxcmp_shop->oxshops__oxadbutlerid->value }].gif/oc=[{$order->oxorder__oxordernr->value }]&sale=[{ $discountnetprice * $currencycovindex|string_format:"%.2f"}]&belboon=[{$oView->getBelboonParam()}]" border="0" width="1" height="1" alt="" id="bbconv"/>
    
    <object class="flash" type="application/x-shockwave-flash" data="https://www1.belboon.de/adtracking/flash.swf" width="1" height="1" >
        <param name="flashvars" value="pgmid=[{$oxcmp_shop->oxshops__oxadbutlerid->value }]&etype=sale&tparam=sale&evalue=[{ $discountnetprice * $currencycovindex|string_format:"%.2f"}]&oc=[{$order->oxorder__oxordernr->value }]">
        <param name="movie" value="https://www1.belboon.de/adtracking/flash.swf" />
    </object>
    <script src="https://www1.belboon.de/adtracking/conversion.jssl"></script>
    <!--Adbutler ende-->
[{/if}]

$oView->getBelboonParam() doesn’t seem to produce any output. Are we missing some sort of configuration option or is there some other problem?
We’ve tried working this out for several days now with no result. The if-condition does return true, but we can’t seem to get the code that follows to work properly.
Flash and cookie tracking work, but session tracking does not.

Also, is it somehow possible to drag custom GET parameters from page to page without losing them?