Stacking Spell Damage Reduction

Hi,

I've been trying to make a passive skill which reduces your spell damage reduction whenever you are hit, up to 50%. So my first approach is, naturally, the BonusMod system. However, I've come to realize that 2 runed bracer abilities don't stack with each others! Only the largest value is taken. So for example, if I want +5% spell resistance, using the BonusMod system I would add a +1% runed bracer and a +4% runed bracer skill together to achieve it; but they don't stack! Is there a way to make them stack or is there an alternative to making a spell like this?

Make a single ability based on the bracer ability with lots of levels.
Then just keep track of what level of the ability a unit should have at any given time by attaching an int to it via cache or using CVs.
Update the level on the unit accordingly, voillah.

That's how I would do it.

but then if I acquire a +spell resistance item that item wouldn't work :(

In fact... if you have that passive skill, that item SHOULD not work.

So is there another spell which provides spell damage reduction? I know Defend does (by making it a passive skill). However, I don't really want the icon it gives >_<

What's wrong with that?
I mean, if you have...
... then you shouldn't have that item work, 'cause you would write so:

"Does not stack with {the name of that skill}."

Just like Talisman of Evasion writes:

"Does not stack with Evasion, and Drunken Brawler."