[XeTeX] Faking an accent when that glyph is unavailable

[Henry de Valence]

I'm writing a document using a font (Aldus LT Std) that doesn't contain the 
character ő (U+0151, LATIN SMALL LETTER O WITH DOUBLE ACUTE).

However I need to use the name "Erdős", and I don't want to use just a normal 
umlaut, because that would be wrong. I have already tried using \H{o} and 
simply 'ő' in the source, but they don't work because the font is missing that 
glyph. I found that the font does have a character for just the accent 
(U+02DD), but I don't know how to get that character or how to put it over top 
of the 'o'. Text-searchability isn't a big issue, because I'm just going to 
print it anyways, so something that looks roughly correct would work fine.

I have tried the following:
Erdo\XeTeXglyph"02dd" s
but it just produces the following text:
Erdo!dd˝ s
which is clearly not what I want.

If anyone knows of a way to fake this, advice would be welcome.
Thanks,
Henry de Valence