Calling all icing experts

[bakedpotato]

I've got 40 fairy cakes to ice for DS's christening. I've bought fondant icing sugar for general icing purposes, and was planning on writing a letter on top in buttercream. Did dummy run and fondant icing seems very soft (even after spell in fridge). Someone has just said if iced in advance (I was planning on doing it some time in advance, a day or so) the letters may seep into the fondant.
Will this happen?
Any way around it?
Would royal icing be better than fondant? (But it's so horrid and hard...)

Yes, bakedpotato, the colours will run.

If you had a piping bag ready with a little fondant icing coloured to whatever shade you want you could quickly pipe the letters onto the wet fondant icing. It would then sink into the surface and dry all together but shouldn't spread into one another like butter icing would.

But you would have to do it really quickly. One or two cakes at a time might be easier.

Fondat tastes alot better than royal, yes the letters might seep into the fondant or the colour might run into the fondant. You could buy that icing in a tube that you pipe out then you could do it the morning before or you could use sweets to write the letters, just stick them on with a bit of icing.

Oh phew, you both sound like you know what you're talking about.
Does royal icing end up rockhard, or can you get around that somehow?
If I iced them in fondant on Saturday, could I get around the running issue by piping the letters (in fondant, I suppose) a few hours before the party on Sunday, or would the same disaster occur?
What would you do?
The in-advance thing is key.

Wouldn't water icing made with hot water work best. You could leave it to get completely dry and then pipe the buttercream on. Perhaps royal icing could be too heavy for fairy cakes.

bp, could you do little letters cut out with ds-name-shaped-letter tiny biscuit cutter type thing? ie with different coloured icing, rolled out in a sheet? sorry if i'm overcomplicating..

Can you pipe letters using coloured royal icing onto greaseproof paper, let them set rock hard and then put them on top of your fondant iced fairy cakes with a blob of white buttercream on the day?

obviously peel the greaseproof paper off the letters!

Waxed paper is better. The icing will stick to greaseproof.

The royal icing letters is a good idea and will be my fallback: thanks.
Some experimental fondant-on-fondant cakes have been in the fridge for a while and no seepage has yet occurred (though a few have disappeared ). Will see what happens overnight.
Definitely won't have room in the fridge though on the day itself. Hope that won't make a difference.
Oh cripes, will it?

What about putting a white chocolate button on the top of the icing and then writing the letter on that?

These are the fantasy cupcakes I'd make were I truly talented. We had some for DD's christening but I'm sure they didn't cost as they do now £2.50 per cake
So, any idea what icing combos Konditor and Cook might be using here?

Princess, not sure I'm up to icing a chocolate button... my eyesight's not what it used to be [squint]

They shouldn't need to be refrigerated. Just keep them in an airtight container in a cool place.