1) Partitioned the stick as follows:
fdisk /dev/sdb
create 1st partition with 512Mb, type W95 FAT32
create 3rd partition with 4Gb, type W95 FAT32
create 2nd partition with remaining space, type Linux
write MBR
do appropriate mkfs for each partition

2) Copied content of image into the stick:
mount -o loop alpine-xen.iso /mnt/iso
mount -t auto /dev/sdb1 /mnt/stick
cp -r /mnt/iso/. /mnt/stick
umount /mnt/*

Disklabel type: dos
Disk identifier: 0x04bfbc80

Device                                               Boot Start    End Sectors  Size Id Type
Downloads/Distributions/alpine-xen-3.7.0-x86_64.iso1 *        0 329727  329728  161M  0 Empty
Downloads/Distributions/alpine-xen-3.7.0-x86_64.iso2        312   3191    2880  1.4M ef EFI (FAT-12/16/32)