Use SKTOOLS
Back at SKTools, click "Category → All" to make the "Input Methods" applet visible and then select it:
Ensure that your favorite SIP is listed in there as "Enabled" (if it's "Disabled", click and hold on it and select "Enable/Disable" at the popup menu). Then, click and hold on it and select "Set as default". If your SIP isn't listed in there at all, it's either incompatible with your device or wasn't installed properly — try reinstalling it again.
Next, locate "Touch Input" in the list and click and hold on it. Select "Registry Explorer" at the popup menu and double-click the "IsSIPInputMethod" folder at the following dialog. Change the value of "Default" to 0:
Close the "Input Methods" applet by selecting "Tools → Main menu".
Scroll a bit further down and click on the "Services" applet. Locate "HTCSipSrvc" in the list, click and hold on it and select "Manual" at the popup menu. This prevents the HTC SIP Service (EzInput's watchdog) from starting automatically on subsequent reboots of your device: