My answer isn't an exact answer, and it may not be useful in your case, but here's what I do in similar situations. This is for when the letter and the "fill" would be the same color, and isn't useful if you want them to be separate colors
I'm using Adobe CS6, which is hopefully the version you are on, if not more recent.
Avoid using the fill tool and instead group vector objects
Your text is a vector. This means it can get as large or small as you want without a loss of quality. This is great.
How to backfill: Use either the Pen Tool (shift+P) or the Shape Tool (shift+U) to draw an image in the negative space you need to cover. Don't need to be exact here!
(I used the pen tool for the triangle in the A, and circles for the other letters).
So the major downfall is it's two layers. To get around this, just put them together in a group. It acts like a layer.
For example, here I've group my triangle layer and my letter A, and applied a few style effects.
[b]my lonely two layers[/b]
[b]combined in a group![/b]
Here's what it now looks like with the layer styles.
But wait, why not combine the layers as a smart object and use that? While you can, it loses the ability to be vector, so I generally tend to using groups. Don't worry, though, as a group pretty much acts like a layer in all ways. For example, here's my group acting as a clipping mask.
End result? Scaled it up to a max resolution and it looks sexy (no outlines here!) Yay for vector objects inside a group!
Here's the steps to repeat
1) Put down the text letter or another object you want to use.
2) "Backfill" this layer by using a custom shape (such as a square or circle). Access the shape tool by using Shift-U.
2a) For complicated letters or images, you may need to use the Pen Tool (Shift-P) to backfill an image. Simply left click and create an outline, which by default draws as a shape.
3) In the Layers Window (F7, but you should always have the Layers window up!) hold down Ctrl and select both layers
4) Add those layer to a group (drag and drop to the folder icon, or press cmd+G).
5) Use your group with layers, create clipping masks above it, or elsewise use that group like you would any layer! (tip: give the group a name to easily identify it in the future)
5a) If you need to, you can rasterize the group by pressing Layer > Merge Down (cmd+E) or by converting it to a smart object.
BONUS: If you want the "backfill" layer to be a separate color, simply place it behind the letter and change it's color via a layer style.