Here it says IV Relenza has been administered in volunteers under study conditions, but not sure how reliable the source is?
http://72.14.253.104/search?q=cache:Zg05irYk6SAJ:www.savethechildren.org/publications/technical-resources/avian-flu/Flu_Tamiflu_Stocking1.doc+Intravenous+Relenza&hl=en&gl=au&ct=clnk&cd=13
Cheers dma