Is it possible to import specific rows from an indexed VCF file with VariationAnnotation, without manually specifying the ranges?

I would simply like to do the following:

# Dummy file
library(VariantAnnotation)
fl <- system.file("extdata", "ex2.vcf", package="VariantAnnotation") 

# This read the entire matrix:
readGeno(fl, x="GT")

# Desired output is this, but without reading in the entire matrix in first:
readGeno(fl, x="GT")[c(1,3,5),]

I realise you can specify a ScanVcfParam argument, but that only takes ranges as input, and not rows directly.

No, the tabix file that is used for random access is based on genomic regions, not rows of the VCF file.