Would I be willing? No, not really. Pay cuts and freezes only work in the private sector when a companies future is potentialy at stake. This is because ultimatimtely all private sector companies are profit making organisations. Loosing 5% of your pay is better than loosing your job.
Here in the public sector, we are paid from the defence budget. The best you could hope for is that the money you donate back would be spent on something useful. I can't say I approve of this though, as it would be tantamount to making guys buy their own ammunition on ops, or fuel, or food, or body armour.
More likely however is that the cash would ultimately end up being wasted away trying to make DIIII work, or auditing travel claims. I get paid less than my civilian counterpart already, I can't see that widening that gap would aid retention much.
So essentialy........No. But maybe I'm just jack