Altostratus
MVPisnt the device certificate stored somewhere on the bigip, (here i believe: /config/httpd/conf/ssl.crt/) couldn't you try to add the intermediate there to it? so just open with vi and paste the intermediate in there. might require a httpd restart or even bigstart restart.
[EDIT] hmmm, looked at apache config and apparently you need to modify SSLCertificateChainFile in the apache config. in the bigip this is found under /config/httpd/conf.d/ssl.conf i believe. not sure how supported it is if you are going to play around with that and what the effect is after an upgrade.