openlayers 2 - Create interactive map with no server

I have managed to build a great web mapping application using tiles created from GeoWebCache and a custom gridset, but I now need to add an overlay to the base maps. The only interactivity I need is a simple pop-up info window that comes from only one of the attributes.

As default the overlay dataset is an ESRI Shapefile which is 180Mb, I have since managed to simplify the dataset using ST_SimplifyPreserverTopology which has dropped the ESRI Shapefile size to 28Mb. However, as a GeoJSON file this is still 78Mb which is just too big.

I then tried CartoDB and loaded the data into a table and then added the vectorlayer in openlayers but the volume of data is still too big and the HTML page crashes.

I then tried GIS Cloud and an external WMS but that is restricted to WGS84 and has no getfeature info option.

I then started looking at Topojson which I think would work really well on my dataset but I dont think there is a way to load a topojson onto a map in OpenLayers 2.12 that I need to use.

My other option was UTF-Grid, so I loaded the data into tilemill and exported a MbTiles which I can extract using mbutil. But of course UTF-Grid only supports EPSG:3857 (web mercator) which is different from my projection, EPSG:27700. So all the .json files are named differently from my underlying cached tiles from geowebcache.

Is there a way to create a UTF-Grid but in a different projection?

So that is the background and feel that I have tried most options that I know about.

So simply I need an interactive overlay layer in an OpenLayers 2.12 map but I cannot use any server like GeoServer/Mapserver or TileStache etc and I cannot have any server side scripting like PHP.

Can anyone offer any other advice??

Thanks