Looks like it might take a 20 guage needle as it is. Or it could be drilled wider. Might be possible to fill with cream or gel. Perhaps KMF is thin enough to go through a needle?
Could make a low profile travel kit. Would have to find some way to adjust the shave angle.
You could easily fill it as is using a pipette and oil, it may need a larger hole to use a syringe but I have blunt tip lab syringes I use at work so I'll see if one fits. The small 1ml syringes I have use a very small blunt tip "needle" and I think it will fit. I've got some extra proraso cream around, my go to, so I think I may just try to to refill it and see what happens. Cremo, Dr carvers, and the gillette proglide tube gel would all work great.
As far as the angle, while the Treo does require you to come at your face horizontally it does have almost the same range of pivot as the regular guard handle does so it's not as much getting used to the angles (it will pivot with you) as it is getting used to more of a "pushing" then "pulling" motion while shaving.