You can do this with Juice Defender -
https://market.android.com/details?id=com.latedroid.juicedefender&hl=en
I found it caused issues with my data connection even when the screen was on though
https://market.android.com/details?id=com.latedroid.juicedefender&hl=en
I found it caused issues with my data connection even when the screen was on though
