You can use ShadowLink hack to make this easier. When you set it up Shadow will add text to the end of the note of a linked Todo (visible in Datebk or Todo) that looks like:
"[[[Shadow: (xxxxxxx) Projectname > Sub-Item]]]".
All you need to do is open the attached note and tap anywhere in the text "Shadow" and it will jump to that item in the Shadow app. From there you can activate the next action.
It's included in the Shadow zip file. There is a version for both Palm OS 4.x and 5.x.