How to name categorical variables?

A follow-on question:

In GLM, the dummy variable encoding automatically drops one value. In other words, if there are n options, it creates n-1 dummy variables.

What’s the best way to achieve this in the general model?
I have a variable defined as:

b = pm.Normal(‘b’, mu=0., sd=0.5, shape=no_dow)
dow stands for “Day of week”.

Is it possible to define this so that:
b[0] = 0
b[1:] = pm.Normal(‘b’, mu=0., sd=0.5, shape=no_dow-1)

Or should I have used something different, like pm.Categorical ? (I’m not familiar with that distribution).