Throwing the coaches red flag???

[allftbl]

......has anyone(solitaire or league play)incorporated the throwing of the red flag or a coaches challenge into their gameplay(challenging a ruling(from whatever system...the shaking of the box??)or result of a play done on the field)
......I want to add this into my universal football league but was wondering if someone else has done this and how they do it (maybe call a challenge,do a roll of the dice,an even number(or percentage)and a play could be overturned and the coach can challenge again,or an odd number and the play stands and team loses a time out?)
......just curious,any info/ideas would be appreciated!