The Tunisie is very different to Sardinia terrain-wise, although both events could be run on an Enduro derived bike with just a bigger tank and the necessary nav. gear - the Tunisie also has an Enduro Cup class where you don't need to comply with all the FIM regs.
I know Desert Rose Racing in the UK have offered assistance and bike rental packages for the OiLybia Du Tunisie in the past - you could drop them a line and ask them for a fly-ride price - that is what Cummo did in 2010 when I was there...
1st bivouac
The fastest bike, is a hired bike...
Jx