You can most likely organize your content in such a way that the filter stays in place. One option could be to wrap your H List box with H Scroll Box
Names Default To Here(1);
New Window("Example",
Outline Box("Picker",
H Scroll Box(
Size(200),
H List Box(
H List Box(Text Box("Label:"), Text Edit Box(Char(213))),
H List Box(Text Box("Label:"), Text Edit Box(Char(213))),
H List Box(Text Box("Label:"), Text Edit Box(Char(213))),
H List Box(Text Box("Label:"), Text Edit Box(Char(213))),
H List Box(Text Box("Label:"), Text Edit Box(Char(213)))
),
<<Set Auto Stretching(1, 1)
)
)
);
-Jarmo