My friend and I are going to attempt to make a large, sitting Lego man. The body will be made of cake and covered in fondant. I keep going through all the steps in my head, and, for the life of me, I cannot figure out how the arms will stay put. I think they'll end up being about 1 1/2 - 2 inches in diameter.

Do you think they'll be too heavy to attach with royal icing? I thought about using skewers or toothpicks, but how do you keep those from pulling through the cake? Any help you can give me would be much appreciated.

I would go with skewers or toothpicks and a little royal icing or melted chocolate glue where the arm makes contact with the body.

For something similar I actually made two RKT strips out of extra hard RKT (slightly crush krispies, reduce butter, heat the mallows an extra minute and pack hard into a tray then cut into strips), these were long enough to touch the board and go right up to the shoulder height.
They were attached to the board with some melted white choc and to the sides of the cake with a harder BC made using half butter, half white veg fat, and i added a little gum paste to the fondant before covering so that all the later fiddling would less likely tare the fondant.
Where the arm is to meet the shoulder cut away the fondant so it is just RKT meeting RKT and use toothpicks and some white choc that has cooled enough to spread thickly and not dribble off.
Support the arms well until the contact dries and support them for transit!

Just thinking about your project; if you make the strips wider at the bottom than the top they will be more supportive and instead of just 'gluing' the strips to the side of the cake maybe cut into the cake and 'glue' them into the gap?
That ended up longer than I thought sorry! but hope it helps

Thank you both so much for your responses! Sugar_N_Spice_Cakes, I like the idea of using both skewers and royal icing. I will definitely do that. Crazy-Gray, don't apologize for the length of your response - I need all the help I can get! All of your advice is much appreciated. I'll be referring back to this thread many times on Monday when we try to put it all together. I'll let you know how it goes.