What you could do is lay in one corner a few flat stones (slates?) on which you place the bowl with food. Than there's almost no sand in your food.
Instead of mineral oil you could use a preparation what is also used for human. For example, lactulose. Perhaps your vet knows it also. I use it (for my humanpatients) in the nursinghome where I work. I know that it is used in reptiles (amongst others in monitors and beardies) with succes.