I don't think any current way will work very well (fast) for what you want to do. Obviously a new feature for /hdel would make it faster, but that won't be added until at least the next version, which could be months down the road. Perhaps a DLL could be made to make it faster... I'm not sure.
Anyhow, because it is slower than you want and a new feature could take months or years before it's added, you may want to consider changing how you're dealing with data. Obviously, your current data setup isn't appropriate for what you want to do with it. Hash tables are great for many things, but aren't always the best option. And, sometimes just changing the hash table format can help out. As I have no idea what you're really using the table for, or how you have it formatted, I can't suggest anything to do with it. I also can't be certain that there even is a better way to deal with the data. I'm just offering this as a suggestion.