Install the font by theme.ini file.

[Install]
Font="misc\Silkscreen.ttf"
FontName="Silkscreen (TrueType)"
Trying this way does not always work tho.
Mixed results, maybe my config...

You can temporarily install the font in mem with lsfonts.
Add these lines in your theme

*NetLoadModule lsfonts-0.1
*LoadFont "$ThemeDir$Misc\silkscreen.ttf"

Again there is issues with some modules
that dont like it this way. Rainmeter for one.

I suggest copying to your windows\fonts dir.
This is the best way to do it.