Empty inner bleed area

Doing a little work for a client's in-house magazine. Usual InDesign page setup: A4 portrait, facing pages, 5mm top, bottom and outside bleed, 0mm inside so I can see the artwork as-is when I drag in large pre-prepared double-page background images upon which to add other elements.

Their printing firm want each page exported individually as A4 PDFs. So I exported with Use Document Bleed Settings checked, and selected the page number for the left half. I chose to include Bleed Marks. Same with the right half.

They rejected the documents. Said they wanted _no crop/bleed marks and no content at all_ on the inside bleed areas. i.e. a 3mm white 'bar' on the inside edges, but with regular 3mm bleed on the other three sides, and no printing marks.

Is this just weird, or a standard request? And, further, how is it best to set this up so it's not a major headache to export stuff to their requirements?

As far as I can make out:

1) If I set up the ID doc with inside bleed of 3mm, when I drag in an A3 background image for the double-page spread, I'll "lose" 6mm of inside edge content when exported: the halves won't be seamless when printed. Plus, I'd need to stretch the image slightly when Placing it in a frame to fit the 4 bleed areas.

2) If I set up the ID doc with no facing pages, designing double-page spreads is a hassle (unless I'm missing something) as I have to cut the background images in half prior to placing each. Plus, I still have to decide what to do about bleed on alternate pages.

3) If I omit all printer's marks on export, the resulting PDF has no bleed on the inside edge when Use Document Bleed Settings is checked, which will result in lost content on the inner edges when trimmed.

4) If I use custom bleed settings in the Export PDF dialog, say 3mm all round, then I do get 3mm of the 'other page' included, but the printing firm don't want this. They want _nothing_ - just whitespace - for the inside bleed. No content there whatsoever.

The only way I've managed to satisfy their requirements so far is via the following convoluted process:

a) Export each page to PDF using option (4) above so I have 3mm bleed all round, with no printer marks.

b) Import a page into Photoshop.

c) Draw a thin 3mm white bar with the rectangle tool and position it over the left or right edge to obliterate the bleed on the inner edge.

d) Save As PDF from Photoshop (which doesn't have bleed settings in the dialog anyway).

e) Repeat for each page.

That's a bind. Can anyone think of a way to set this up more seamlessly so I can design in double-page spread nirvana, yet export to PDF with a 'blank' 3mm inner bleed area?

Thank you in advance for any ideas.