I bow my head, but I do not pray with everyone or clasp my hands. I know some people would be uncomfortable even with that, and if you are I would just sit quietly to be polite.
I don't think you need to make a statement or scene about it. If you think a prayer is inappropriate in that scenario, wait until the end of the meeting and talk to the person who initiated it.
I felt really awkward about this for a long time, but as long as you aren't disruptive no one has any reason to bother you.