We have had good results with the Masamune-Roush (Blanchette MA et al., Tetrahedron Letters 1984 25(21):2183-86) variation of the HWE, which is suitable for substrates that would not tolerate a strong base. Typically people use LiCl or LiBr as the catalyst, and DIPEA or TEA may be used. If the lithium ion chelates the phosphorus-containing molecule (there is a second oxygen that can bind the Li+ ion in all of the examples I can think of offhand), the pKa is lowered. However, your reactants are considerably different versus ours, and our experience is probably not applicable. I have also seen an FMOC-protected amino acid used in a HWE reaction with LiHMDS. IIRC the yield was not great. One wonders if there was some loss of the FMOC-group.