There is a console command, "mp", which allows you to set a known character's movement points to anything between the hard-coded minimum (0) and the maximum (I don't remember, it's agent type specific) as in the example below.
Code:
monitor_event FactionTurnStart TrueCondition
console_command mp our_character_label 0
terminate_monitor
end_monitor
I don't remember if mp is a set value or additive command. If the latter, you would need to know how many move points the character starts with then subtract >= that value using mp.
If you wanted the character to be stuck every turn, you would need to loop this monitor and continually set their move points to 0.