Just a thought: Driving is an automatic action, especially on a commute journey that we know well.
So why not doing sadhanas... after all, we can talk when we drive, proof that the mind can multi-task combining:
1. the automatic action of driving,
2. the prayer and even the visualization.
What can't be done while driving is anything that occupies the hands, like holding a phone, holding a hamburger, sending sms, etc...
So for as long as we do sadhanas without using bell and damaru, and as long as we know the prayers by heart, I do not see the problem... do you?