DD wants her "boyfriend" at her birthday party

I hadn't expected to deal with this for a few years yet, but my almost 4 yr
old decided on a Fairy princess themed birthday party, which we're having
off site at a place which does dress up tea parties. Since she only has a
handful of girls in her class, we'd planned on inviting the girls and a few
close friends, most of whom are a little older than DD.

However, now that we're about a month out and sending actual invitations,
she's told me that she wants a specific little boy in her class at her party
as well because "He's my boyfriend, and he'd be sad if he wasn't invited".
This little sweetheart is the youngest child in the class (just turned 3
right at the end of September, in a class where the kids had to be 3 by
October 1), and for whatever reason, latched on to DD at the beginning of
the year. Their teacher comments that DD's basically his big sister-she
often "translates" for him, helps him with his backpack and coat, plays with
him, and just plain runs interference with him since he's a little lost with
the rest of the preschoolers, and often "teaches" him and walks him through
the centers and basic academic stuff (which is also working well for keeping
DD busy-so far, having a child who tests on a high 2nd grade level on
academics in the preschool classroom hasn't been a problem at all-in part
because of this peer relationship which has developed). We've had a few
playdates outside of preschool, since his grandmother has him in the
afternoons and she doesn't live very far away from us, and it's the same
thing. So, I guess it makes sense that she wouldn't want to leave him out,
but I kind of wish she'd picked a less stereotypically girly party. I just
have a hard time picturing this little guy who loves trucks and farm
machinery in a room painted to look like Barbie's dream castle made little
girl sized, where the main entertainment planned is dressing up in the large
collection of princess costumes, making magic wands and tiaras, and taking
pictures of the "princesses" dressed up, followed by "tea" and cookies!

Anyway, does anyone have suggestions for including a barely 3 yr old boy in
a party where the rest of the participants are girls ranging from 3 1/2 to
5? I've already warned grandma that the guest list is 8 little girls
(including DD), plus her grandson.