The difficulty of that trick vacman is the small issue of ensuring that it is a short swing link stock formation.... and as far as I'm aware there aren't diagrams of bogie type...
Although a candidate for a Weymouth
HST▸ could be an additional 0935 London Paddington to Weymouth via Westbury, calling at:
0735 London Paddington
0803 Reading
0850-0852 Westbury
0902 Frome
0916 Castle Cary
0934-0940 Yeovil Pen Mill
0948 Thornford
1002 Yetminster
1007 Chetnole
1019 Maiden Newton
1031 Dorchester West
1040 Weymouth
It would then in turn be able to operate the 1110 to Gloucester as far as Westbury (assuming times don't change during the summer tt) - running on timings (slightly modified to allow for HST acceleration:
1110 Weymouth
1115 Upwey
1122 Dorchester West
1135-1141 Maiden Newton
1149 Chetnole
1153 Yetminster
1156 Thornford
1204 Yeovil Pen Mill
1218 Castle Cary
1223 Bruton
1237 Frome
1247 Westbury (connects into 1252 unit forward)
Then it could maybe work an additional Westbury - Southampton Central (all in the name of additional capacity while using spare stock!)
1309 Westbury
1318 Warminster
1340 Salisbury
1401 Romsey
1415 Southampton Central
1433 Southampton Central
1443 Romsey
1503 Salisbury
1523 Warminster (replaces 1528 Warminster - Great Malvern to Westbury)
1526 Dilton Marsh (single door only?
)
1529 Westbury
Then...
1536 Westbury
1546 Frome
1557 Bruton
1603 Castle Cary
1616 Yeovil Pen Mill
1619 Thornford
1622 Yetminster
1625 Chetnole
1637 Maiden Newton
1652 Dorchester West
1700 Upwey
1706 Weymouth
This then allows for
1827 Weymouth
1839 Dorchester West
1856 Maiden Newton
1917 - 1920 Yeovil Pen Mill (1749 off Temple Meads will have to run 2 mins later)
1933 Castle Cary
1953 Westbury
2042 Reading
2110 London Paddington
Not really great timings on the return but that's really the best path that I can see