Do you workout on Saturday at the same time, or possibly 'sleep in' and workout a bit later ?
Do you do Lantus 1/day or a split dose ? If doing a split dose, you might be able to reduce just the morning dose only on Saturday.
On Saturday, what do you do after your workout ? I often go low doing housework or running errands, and usually turn down the basal on my pump. In your case on MDI, you may need to have more snacks.