Widget size half of the screen

Hi.. i have already developed a application which reads incoming sms. I understand that invoke the application automatically i need to sign the application. Now once i signed the application and it's invoked automatically on incoming sms, i want to show an alert in the middle of the screen keeping the phone native backgroud as it is. Once i select ok/open the alert then i go to the application or generate the full screen application. now i want to know can i show the desktop or alert in a specific size keeping the phone native backgroud as it is?

This isn't possible with J2ME. All canvas or screen-based user interface components are designed to fill the screen (excluding possibly the native time, battery level, signal strength etc. indicators).

Thanks buddy..